Crop Improvement and Practices for Eco-Friendly Environments – The Examples in Taiwan

Crop Improvement and Practices for Eco-Friendly Environments – The Examples in Taiwan

Published: 2020.07.09
Accepted: 2020.07.08
15
Department of Horticulture, Chiayi Agricultural Research Institute, Taiwan Agricultural Research Institute
Department of Agronomy, Chiayi Agricultural Research Institute, Taiwan Agricultural Research Institute
Crop science Division, Taiwan Agricultural Research Institute
Department of Agronomy, National Taiwan University

ABSTRACT

The potential risk of a crop disease can be determined by considering the three components of the “disease triangle” that may combine to cause its occurrence: pathogen, host, and environment. An outbreak of a crop disease requires the presence of a virulent pathogen in sufficient quantity to initiate infection, the presence of a susceptible host for the pathogen to infect, and the occurrence of favorable environmental conditions for the growth and proliferation of the pathogen. Human activity can modify the components of the disease triangle, and these anthropogenic effects may cause the emergence or resurgence of crop diseases in a particular region or country. For example, many diseases depend on high levels of moisture to promote plant growth and allow disease development. Although the cultural practice of irrigation is used for production of crops in many countries, the additional moisture it provides may result in negative effects in the form of increased risks of crops to diseases. In Western Canada, the emergence of the three high profile diseases, Verticillium wilt of alfalfa (Verticillium albo-atrum, Vaa) in the late 1970s, bacterial wilt of bean (Curtobacterium flaccum faciens pv. flaccum faciens, Cff) in the late 1990s, and white mold of bean (Sclerotinia sclerotiorum, Ss) in the late 1980s, was mainly due to production of these crops under irrigation. Although producers have little or no control of natural rainfall during the growing season, they can modify their irrigation practices to help reduce disease development in irrigated crops. Since Vaa and Cff are quarantine pathogens in Japan, Taiwan and China, and Ss is a quarantine pathogen in Japan, the focus of this review is to discuss the effects of some anthropogenic and epidemiological factors on emergence and spread of these diseases in North America and measures to prevent introduction and spread of these high profile pathogens in Asian countries.  The agricultural productions and developments are greatly influenced by environments which are complex because of various geography and island-type climates, and recently by global climate change and the globalized and localized of agricultural products in Taiwan. For long-term eco-friendly environmental agriculture toward sustainability agriculture, breeders must set breeding goals and selection indices for new cultivars with resistances/tolerances to biotic and abiotic stresses strategies according to crop physiology and stress damaged symptoms which are able to be applied to crop practice in fields. In this study, we focused on the breeding aspects of rice, cereals, vegetables and fruit crops for eco-friendly environmental agriculture. The new rice accession bred by marker-assisted breeding (MAS) exhibits drought tolerance, leading to water-saving practice with reduction of irrigation water. The early curding accessions of broccoli by untrogression of early-matured gene to elite broccoli with MAS can be shortened cultivation time, leading to avoid biotic stress damage, reduce practice cost, and increase the land utilization simultaneously. Another useful way to increase the yield is to prolong the shelf life of pineapple, which can reduce food lost. The exploitation of double haploid breeding materials in maize could broad genetic variations of germplasm resources and also accelerate breeding generations, beneficial for obtaining new varieties of eco-friendly practices in maize. Because of state-of-art technologies in high-throughput genotyping and uncovering gene/loci of agronomic traits, MAS and genomic selection (GS) accelerate breeding efficiencies to obtain new varieties nowadays. In addition, to achieve the goal of eco-friendly environmental agriculture, we promoted stress-resistant rice varieties and practiced rice cultivation with reduced fertilizers and pesticides. Therefore, we achieved these goals by breeding, cultivation practice and the prolongation of agricultural products in Taiwan.

Keywords: Broccoli, Drought tolerance, Gene pyramiding, Maize, Marker-assited selection, Pineapple

INTRODUCTION

By 2050, the world population is projected to be 9.8 billion and global grain demand is projected to double (Tilman et al. 2002). On the other hand, lands for agricultural production would dramatically be reduced because of urbanization and industrial factories. In the last few decades, semi-dwarf wheat and rice varieties evoked the Green Revolution and relieved hunger. However, traditional agricultural practices have heavily relied on lots of chemical fertilizers, pesticides, and herbicides, resulting in damaged environments. Recently, many studies addressed regional and global factors affecting the tradeoff of food security and environmental sustainability (West et al., 2014).

Site-specific strategies regarding agricultural sustainability were proposed. Approaches directly related to crop production were as follows: (1) Integration of ecological and biological processes for instance nutrient cycling, N fixation, soil regeneration, predation, and parasitism into food production processes; (2) Enhancement of crop production per unit time, area, and major inputs such as water and fertilizers (Pretty 2008; Mishra 2013; Shah and Wu 2019). The triangle consisting of production, environment, and landscape values provides insight into future environmentally friendly agricultures (Borch et al. 2005). For production, major factors including precision farming with smart agricultural technology, plant gene technology, and cultivation and soil fertility are involved. For eco-friendly environments, using environmentally friendly substance instead of pesticides and herbicides is suggested. For landscape, increasing the biological diversity in the field is recommended. On the other hand, agriculture production is encountering severe biotic and abiotic stresses because of global climate change. Unbalanced water circulation results in unpredicted precipitation, and distinct dry or raining seasons. In addition, ambient temperatures fluctuate severely. These environmental factors have a great impact on crop production. With climate change, new strains of pests and pathogens arose and challenged the agricultural practice of integrated pest management (IPM). Management practices and breeding programs are two key fields that keep food security and eco-friendly environments under the 2050 scenario (Tester and Langridge 2010).

The breeding goals for food resilience and future farming for eco-friendly environments were described in three aspects: (1) to improve crops’ tolerances to abiotic stresses, such as high temperature, low temperature, drought, and flooding; (2) to improve crops’ resistance to biotic stresses, such as pathogens, pests, and nematode; (3) to adjust flowering time for crop rotation to increase land usage per unit, for reduction of environmental impacts on production, for reduction of practice costs such as water, fertilizer, and energy; (4) to prolong crop storage for reduction of food waste. A six-step process to develop new crop cultivars for increasing annual yield was proposed under the scenario of marker-assisted selection: (1) envision changes in crop management; (2) identify useful agronomic traits from germplasm collection; (3) identify genes/quantitative trait loci (QTLs) by pedigree mapping and/or genome-wide association studies (GWAS); (4) generate genetic diversity by mutagenesis if necessary; (5) breed new cultivars by MAS; (6) implement new cultivars infield practice (McKersie 2015). This strategy has been widely applied in private and public sectors. Because of the advantages of genome sciences and next generation and third sequencing technologies, high-throughput genotyping has been applied to unveil useful genes from natural germplasm and consequently to breeding programs subjected by MAS. MAS is a very powerful and popular strategy for crop improvements. We also applied MAS to adjust the flowering time of rice, drought tolerance of rice, salt tolerance of rice, the flowering time of broccoli (Chen et al. 2010; Chen et al. 2012; Lien et al. 2016; Lin et al. 2018).

CASE STUDIES IN TAIWAN

Tropic of Cancer is across Chiayi, Taiwan, and the highest mountain in Taiwan, Yu-Shan (Jade) Mountain at 3952 meters above sea level. Thus, the climates of Taiwan are varied, including tropical, subtropical, and temperate. The precipitation is not across the whole island and not even the whole year as well. Thus, many kinds of crops continue to thrive, and agricultural practices are very diverse depending on crop cultivations in diverse geographic locations and environments. On the other hand, different breeding goals are set for different crops. Herein, we take four crops, i.e. rice, broccoli, pineapple, and maize as examples to understand how breeding goals and practices achieve sustainable environmental agriculture for a healthy planet. 

New rice varieties with multiple resistances/tolerances to biotic and abiotic stresses

Rice is the major crop in Taiwan, whose total cultivation area for two crop seasons was ranged 243,862.280 ~ 274,677.320 hectares in 2010 ~ 2017 (Council of Agriculture, http://agrstat.coa.gov.tw/). The breeding goal was to increase yield in the 1970s and to improve grain quality in late 1980. Nevertheless, new varieties with multiple resistances/tolerances to biotic and abiotic stresses are under-developed for eco-friendly environmental agriculture.

We used natural germplasm such as wild rice, landraces of upland rice, and other exotic germplasm to unveil resistant genes for rice improvement. In addition, we also applied sodium azide (SA), ethyl methane sulfonate (EMS), and ethylnitrosourea (ENU) to create mutant pools of popular cultivars. Large-scale selections were applied to the tolerance to abiotic and biotic stresses. Germplasm, once identified with resistant genes, were backcrossed to elite cultivars for generating introgression lines, which were ready to be subjected to further breeding programs as advanced breeding lines. The strategies used in the Department Agronomy, Chiayi Agricultural Research Institute, Taiwan Agricultural Research Institute (TARI), Chiayi were indicated in Figure 1A.

Since biotic and abiotic resistances are influenced by environments and are not easy to be evaluated at various growth stages, marker-assisted selection (MAS) based on DNA marker genotypes can reduce interference of environment factors in traditional breeding. For example, the researchers of International Rice Research Institute (IRRI) employed MAS to improve elite cultivars for resistances to submergence, salt, and blast (Neeraja et al. 2007; Thomson et al. 2010; Jiang et al. 2012). To promote efficiency and accuracy of multiple stresses, gene pyramiding of multiple good traits by MAS is also welcomed to improve elite cultivars. Because drought tolerance is a very complex trait and the standard of drought tolerance assessment was not well-established, breeding of drought-tolerant rice had been difficult. However, various concentrations of PEG-6000 (Polyethylene Glycol 6000) are used to adjust osmotic pressures to mimic drought stresses. The drought tolerance and avoidances were assessed by root morphology, root system architectures, and root depth (Steele et al. 2006; Uga et al. 2013). The QTLs of drought tolerance, qtl12.1 and DRO1, and the QTLs of salt tolerance, SKC1 and Saltol, had been applied to rice breeding (Ren et al. 2005; Bernier et al. 2007; Kumar et al. 2007; Uga et al. 2013; Kuo et al. 2013).

The indica variety with drought tolerance, Hanyu 115 (HY15), was used to map QTLs of drought tolerance, and uncovered two QTLs located on chromosome 12 (Hsu. 2012). The drought tolerance of HY15 was introgressed in aromatic rice CNY911303 by MAS, and the new rice accession was tolerant to drought for whole growth and reached to 5,000 tons yield per hectare (Kuo et al. 2015). Meanwhile, the salt tolerance line, CWY981126, was crossed to HY15 and backcrossed to WY981126 for two generations to pyramid salt and drought tolerances to solve soil salinity accompanied with drought (Lien et al. 2016). In addition, bacterial blight and blast resistance genes of advanced breeding lines were introgressed to Taiwan elite cultivars by MAS. For increasing the applications of rice, we also pyramid other traits, such as gold endosperm, giant embryo, high-zinc, high-Fe, to increase micronutrients. Thus, we propose the strategy of breeding rice with multiple resistances and good traits in four steps: 1) pyramiding resistance/tolerance to biotic and abiotic stresses by MAS; 2) enriching rice micronutrients by mutation breeding; 3) integrating all beneficial traits from Steps 1 and 2 to obtain multiple resistant genes with enriched micronutrients; 4) introgressing useful genes from sorghum and corn for drought tolerance (Figure #1B).

Broccoli with early curding for shift production

Flowering time, the transition from vegetative to reproductive growth, is crucial for plant adaptation to various latitudes and is considered an important trait for maximum crop yield and quality. To dissect genetic factors regulating flowering time contributes not only to elucidate the floral transition at the molecular level but also to breeding new cultivars for cultivation in a wider range of environments with predictable growth duration and harvest time. To adjust the flowering time to optimize crop production will support food security and food resilience. In addition, new varieties with various flowering time provide shift production and crop rotation to increase the land utilization, one way for eco-friendly environmental agriculture.

Broccoli (Brassica oleracea, var. italica), cultivated for its thickened edible inflorescence1, has also gained attention for containing rich anticancer compounds, glucosinolates. However, broccoli production is restricted to limited areas or cool seasons because the flowering is triggered by facultative vernalization. Broccoli curds properly from vegetative to floral meristems and forms thickened ‘curds’ under low temperature. High temperature impedes differentiation of floral meristems and results in uneven-sized floral buds. Characteristics of non-vernalization and heat tolerance are compulsory for broccoli cultivation under global warming, and for extending cultivation to subtropical zones, such as Taiwan and Southeast Asian countries. To identify genes/QTLs affecting flowering time is important for investigating mechanisms underlying the vegetative-reproductive transition in plants, and also can provide information and tools to accelerate marker-assisted selection (MAS) to breed new varieties and broaden cultivation seasons and areas.

Early curd induction and heat tolerance are important traits for broccoli and cauliflower breeding in Taiwan and other Southeast Asian countries. A breeding program aiming to develop heat-tolerant broccoli hybrids adapted to the eastern United States was launched in the early 1990s. In our study, 112 advanced broccoli breeding lines selected in Taiwan, subtropical regions, provide a unique genetic resource to uncover new genes/QTLs. By bi-parental mapping, 4 DCI QTLs and 3 CQ QTLs accounted for totals of 56.28% and 33.02% of variance in curding time and curd quality (Lin et al., 2018). The location of qDCI-3/qCQ-3 corresponded to BoFLC3, and three BoFLC3 haplotypes were identified in these advanced breeding lines of broccoli. Alleles conferring earliness and good curd quality are both necessary to commercially successful elite cultivars. In this study, BLM29 provided favorable allele, promoting curding by 3.81 days and reducing curd leafiness by 0.44 degree, from qDCI-6/qCQ-6 (Lin et al., 2018). After 3 backcross generations with marker-assisted selection (Figure 2A), four selected BC3F1 individuals exhibited earlier flowering time than the elite parent line BLM25 but possesses similarly superior horticultural traits (Figure 2B).

Strategies for improving storage and transport in pineapple breeding

Reduction of food wastes by prolonging food storage for transport through long distances is one of the keys to food security. If the produced fruits and vegetables are resistant to rot, then few lands or less agricultural practices are required to meet the demands. In order to enhance spatial-temporal diffusion harvesting and to avoid the cultivated risks, we currently adjust fruit and vegetable crops production to the proper climatic conditions and harvest seasons. In Taiwan, pineapple flower bud differentiation naturally starts from late November to the middle of January, and 80% of Taiwanese pineapples are ready for harvest in June to August. This highly affects the price of fresh fruit market by production overcapacity. However, there is a need to import pineapples during the period from August to February since winter fruits are highly acidic. In 2016, the import volume and value reached 4,106 tons and $NT21,588 (Kuan et al. 2017).

Pineapple (Ananas comosus L. Merr.) is a herbaceous perennial tropical plant that belongs to the family Ananas, Bromeliaceae. The cultivation of pineapple is confined to warm temperature, sunshine-sufficient, and stable seasonal rainfall areas. Pineapple is known for growing remarkably well under drought conditioning, yet, it doesn't come up well under low storage temperature. Pineapple fruits become mature 18 months after planting, so the quality of fruits is highly affected by annual climatic conditions. At present, due to cultivation techniques and variety adaptability, pineapples can be grown and harvested all year-round in Taiwan. Under seasonal changing of precipitation and temperature conditions, breeding for wider tolerance and extending the shelf life of the crop become important issues. Pineapples are mainly grown in southern Taiwan where the precipitation extremely changes between rainy and dry Sunburn, skin damage under harmful strong sunshine and humidity, is usually followed by pathogenic invasion and fruit rotting, as micro-environmental conditions extremely affect fruit appearance and quality (Lee et al. 2011). In the winter, the cold damage caused by low temperature leads to the abnormal shape of pineapple crown, inflorescence, skin coloration, as well as fruitlets hardening, and fruit browning. After two weeks of storage under 5°C and four days of room temperature shelf life, the inner core of pineapple fruit and 50% of core boundary were browning (internal browning, IB), and the fruit lost commercial value. The storage under 12.5 °C could be extended up to four weeks (Syue et al. 2009). Pineapple breeding for wider adaptation to lower storage temperature, and longer shelf life makes it possible to expand the export market and fill the lack of cold-weather fruits.

We examined the fruit appearance, fruit tapping sound, TSS/TA ratio, the degree of mildew and browning as the resistance index to storage and transport of pineapple, in order to choose and cross the ideal donor parents to enhance storage and transportability of the current varieties. The effects of related quantitative trait loci will be further analyzed during the selection process. The strategy of marker-assisted selection might improve selection efficiency by declining the impact of phenotypic selection under different environments and cultivation practices.

Establishment of double haploid lines for accelerating maize breeding

Maize (Zea mays L.) is one of the most important crops in the world. Human population growth, global warming and climate change force breeders to rapidly come up with new maize varieties which are high-yielding, widely-adapted to meet the demands of human consumption, livestock fodder.

Breeding inbred line is the first and critical step in new variety breeding process. Selection of ideal inbred line plays an important role in the development of hybrid maize. In the context of traditional breeding process, multiple labors, materials, and time contribute to the genetics fixation after several generations of self-pollination. The inbred line Stock6 with 2.3% induction rate was described by Ed. Coe in 1958, and induction rates have been further increased to higher than 8% through the practical production of large amount of doubled haploid (DH) plants and the development of RWS, UH400 and Tails (Prasanna et al., 2012). DH technology has been developed and applied to doubling haploid plants in maize breeding. Compared to conventional inbred line breeding, the induction line as pollen donor pollinates the breeding materials and produces haploid seeds on the ear. After artificial selection and treatment with colchicine, the haploid plants are transplanted into the field and homozygous lines can be produced by self-pollination (Prigge and Melchinger, 2012). DH technology is the most rapid way to provide homozygous lines. The gametes in segregating population are fixed without dominant effect. The breeding potential in genes to target traits can be directly evaluated. In the beginning of selection, total genetic variance can be obtained while the inbred lines and testcross lines are with the largest genetic variance. There is great improvement of selection efficiency and accuracy by using DH plants to assess the impact of environmental effects on phenotypes under different environments (Rober et al., 2005).

In order to improve maize breeding efficiency, the Taiwan Agricultural Research Institute (TARI) has introduced RWS and RWK76 which have high induction ability from Hohenheim University in Germany in 2014. After three-year study of marker-assisted selection, self-pollination and test-cross, the haploid induction line with 10% induction rate is produced to adapt to the weather in Taiwan and get over cross-incompatibility conferred by Ga1-S in maize (Table 1). Since 2015, conditions and methods for the production of DH in the field has been established in TARI. Sixty DH maize ears can be produced in cost-effective and labor-saving strategy within ten months. Future work is planned to continuously optimized DH technology to establish maize DH seed bank with high genetic diversity, and to apply to quantitative trait loci and genetic maps in breeding scheme for drought-tolerant, heat-tolerant and flood-resistant maize. New varieties might be expected to respond to abiotic impacts under climate change and reduce the impact of meteorological disasters on Taiwanese maize cultivation.

Table 1 The haploid inducing rates in haploid inducing lines established in TARI.

Line

Average haploid inducing rate*

Standar deviation

THI-A

0.101

0.045

THI-B

0.101

0.035

THI-C

0.095

0.045

THI-D

0.098

0.032

THI-E

0.091

0.028

THI-F

0.100

0.032

THI-G

0.116

0.054

RWS

0.117

0.085

Practice of the new rice varieties/accessions for eco-friendly environment

According to the breeding strategy described previously, drought tolerant rice accessions were selected by using PEG-6000 hypotonic solution at seedling stages and drought test in fields. After 6-year breeding for drought tolerant selection, the yield components of the 7 accessions of 108 drought tolerant lines exhibited significantly different under condition of no irrigation since 1.5 months after transplantation. Three accessions had poor yield as compared to it recurrent parent, a japonica rice Taikeng 9 (TK9) which is one of popular varieties with premium grain quality (Table 2). Four drought accessions produced more than TK9, among which DT3 produced 7,669 kg/hector, twice more than TK9.  Thus, DT3, inherited drought tolerance characters from its indica parent, grew very well under limit irrigation, indicating DT3 has potential to keep food security encountering drought climate and/or applying less irrigation for eco-friendly environment.  In addition, the genome composition of DT3 has up to 96% similarity to TK9 because of marker-assisted backcross (MAB). Even DT3 was cultivated under insufficient irrigation, its grain appearance of was still translucent with few chalkiness, and palatability was the same as TK9 that DT3 had 19.6% amylose content (AC) and 5% proteins.

Table 2. The yield of components of the elite cultivar, TK9, and 7 drought tolerant accessions in the first crop season, 2014 spring.

Accession

PLa

PW

PN

SN

Fertility

WS

Yield

Yield index

TK9

18.25 bc

1.22 fg

14.92 a

102.19 def

31.5ef

25.82 ab

3713 efgh

100.0

DT3

18.76 ab

3.17b

11.42 bc

140.68 b

75.5 bc

25.20 abc

7669 a

206.5

DT1

18.19 bcd

1.32 fg

12.00 bc

114.41 de

30.8 ef

25.79ab

1392 ij

37.5

DT5

16.71 bcd

2.43cde

12.17 bc

100.22 ef

82.5 ab

26.16ab

5359 bcde

144.3

DT17

18.65 b

1.22 fg

11.92 bc

136.54 bc

23.5 f

23.30 c

1467 ij

39.5

DT18

18.55 b

1.80 ef

11.42bc

120.30 cd

42.0e

26.54ab

2328 ghi

62.7

DT38

15.82d

2.51 bcd

12.83 abc

99.65 ef

94.8a

24.83 abc

5536 bc

149.1

DT56

16.55bcd

2.36cde

13.33 ab

99.99 ef

83.8 ab

25.40 abc

5449 bcd

146.8

a the full names of the abbrevations are, PL pancile length; PW: panicle weight; PN: panicle number; SN: Spikelet number; WS: Weight of 1000 seeds.

The drought tolerant accession, DT3, was organic practiced for large scale cultivation for 2 years at Liou-Jiao Township, Chiayi in 2016.The field test indicated that DT3 performed better than traditional practice at the aspects of growth, agronomic traits, yield and grain quality. In the first crop season 2017, DT3 and other 4 cultivars, TN11, TNG84, TK9, and TNG82, were cultivated in Xikou Township, Chiayi County. The practices were to apply fertilizers of 120, 180, 240 kg/hectare and different irrigation at every other 4, 10, and 18 days. The yield of DT3 was at the average of 9,635 kg/hectare which was better than the other four varieties, especially TN11, the leading variety in Taiwan (Table 3). In the second crop season 2018, DT3 was practiced with reduced chemicals in Er-Shiue Township, Changhua. By 83% reduction of chemicals, DT3 exhibited high resistance to blast but weak resistance to bacterial blight and brown planthopper. Overall, DT3 performed well, indicating potential for eco-friendly environment practice with less chemicals.

Table 3. The applied fertilizers and yields of 5 rice cultivars planted in Xikou Township, Chiayi County, in the first crop season, 2017.

Accessions

Amount of Fertilizer (kg)

Yield/hectare (kg)

TN11

120

7,670

 

180

8,568

 

240

8,609

TNG84

120

9,530

 

180

9,263

 

240

7,372

TK9

120

8,651

 

180

9,279

 

240

9,455

DT3

120

7,907

 

180

10,936

 

240

10,061

TNG82

120

8,329

 

180

7,398

 

240

9,234

New varieties with multiple resistances to biotic and abiotic stresses are evitable for eco-friendly environments. Tainung 81 (TNG81), bred by Chiayi Agricultural Research Institute, Taiwan Agricultural Research Institute (TARI) and released in 2017, is known for its resistance to biotic stresses, has high yield and premium grain quality. In the first crop season 2006, Taikeng 2 (TK2), a japonica variety with premium grain quality was crossed with CNY902036, an advanced breeding line with resistances to pests and disease, ideotype of plant morphology, and anti-lodging. After 5 generations of selection by pedigree breeding, the accession CNY981027 was selected in 2009 and was registered as TNG81 in 2017. TNG81 exhibited highly resistant to leaf and panicle blast disease and mild resistance to planthopper. Thus, the application of chemical controls is expected to reduce 1~2 times, leading to eco-friendly environment with less cost.

Tainung 82 (TNG82), bred by Chiayi Agricultural Research Institute, Taiwan Agricultural Research Institute (TARI) and released in 2011, is known its good palatability and taste. In 2000, Tainung 67 (TNG67) was induced by sodium azide, and single seed descent (SSD) selection was applied. After 11 years, TNG82 was registered and recognized as good palatability which is similar to the Japanese leading variety, Koshihikar and low protein, 4.5-5%. TNG82 did not exhibit high resistances to blast, bacteria blight, brown planthopper and sheath blight. Nevertheless, low nitrogen application was suggested to produce low protein contents of TNG82, leading to eco-friendly environment.

In the second crop season 2018, the practices of TNG81 and TNG82 with reduced chemicals were executed in Chiayi (Figure 4A, B). TNG81 was cultivated in Field A where chemical spray was applied three times with 3.4 kg/ha in total and Field B where no chemical spray at all. TNG82 was cultivated in Field C where chemical spray was applied three times with 2.6 kg/ha in total and Field D where seeds were coated with chemicals in total of 2.1 kg/ha. As compared to traditional practices, the chemical reductions were 83, 100, 91, and 93%, respectively, in these four fields. The symptoms of rice blast, sheath blight, planthoppers, and rice leaf folders were below threshold, which were acceptable, in all fields except for rice leaf forlder which was severe in Field C (Figure 4C, D, E, F).  As the results, the application of integrated pest management (IPM) to elite cultivars with resistances to biotic stresses can reduce chemicals, and contribute to towards eco-friendly environment. 

CONCLUSION

The climate change in Taiwan, located in the tropical and subtropical zones, is more severe than global scale. The abnormal and unpredicted weather causes various disasters which are relatively frequent and severe, especially in agricultural development and production. In order to achieve eco-friendly environmental agriculture, we must start from breeding, and focus on agricultural practices, field management, and reduction of agricultural losses. The crop breeding goals are spatially and temporally different to meet diverse natural environments and social demands. To relive the burden of the earth rising from agriculture, it is necessary to reduce resources input in agricultural practices, such as irrigation, fertilizers, and pesticides. The breeding objectives should be toward increasing resistances/tolerances to abiotic stresses and to reduce agricultural losses by regulating production period and prolong shelf-life of crops. Utilizing natural germplasm and segregating populations or mutagenesis methods to explore resistance-related genes, and set different environmental stress conditions to further establish indicators for stress resistance. Moreover, performing pedigree mapping or/and genome-wide association mapping with high-throughput genotype data to obtain qualitative/quantitative trait loci for breeding. Accordingly, precision breeding may be achieved by integrating hybrid breeding with molecular-marker assisted selection or genomic selection, or to obtain new varieties by molecular breeding techniques, such as genome editing. 

Under the practice of water-saving cultivation, the yield of drought tolerant rice, DT3, which was bred by MAS, was much higher than that of major varieties in Taiwan, especially for TN11, well-known as its high yield. Exploring the early-curding and heat-tolerant genes of broccoli in subtropical regions is very helpful for broccoli breeding. The early-curding broccolis bred by MAS are expected to shorten cultivation time of broccoli, reduce the use of production resources, and increase land utilization. In addition, the early-curding broccolis are feasible to manage production periods and are easily rotated with other crops as well. The long-shelf-life pineapple germplasm has been screened from seedbank, and QTL mapping will be conducted as well. MAS will be applied to pineapple breeding in the future to reduce agricultural losses for which there is another way to increase the yield. Maize breeding has s a long way to go, however, with the development of DH technique, the genetic diversity can be effectively increased as well as accelerating the breeding program of maize, leading to breed new varieties for eco-friendly practices. Two japonica rice varieties, TNG81 bred by traditional breeding and TNG82 bred by mutagenesis, could still produce the same or more yields under practices with less pesticides and fertilizers. From these view points of view, the development of eco-friendly environmental agriculture has been successfully progressed and committed to sustainable agriculture as well in Taiwan.

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