|11-900NC Project Manager: D. C. Jones|
DEVELOPING THRIPS TOLERANCE IN UPLAND COTTON
Vasu Kuraparthy, North Carolina State University
Cotton (Gossypium hirsutum L.) is grown on nearly 10 million acres across the cotton belt of the United States. One of the early-season insect pests, thrips, can cause significant damage to cotton across the US cotton belt. Thrips damage cotton seedlings by puncturing and rasping the outer cells of young leaves and buds. Damage frequently results in ragged-looking plants with crinkled leaves. This damage can stunt growth, resulting in fruiting at higher positions, maturity delays, and reduced yields. Because thrips have the potential to cause significant yield losses and maturity delays, this pest must be controlled annually. As a preventive measure aldicarb (Temik) is applied as an at-planting soil systemic insecticide in more than 90% of the cotton acreage as an early control strategy for thrips and nematodes. However, it was recently announced that the highly effective thrips-controlling insecticide, Temik, would be phased out by the year 2014 because of its toxic effects in the environment. This can result in a handicap for controlling thrips. Developing a thrips tolerant cotton gerplasm would help fill the gap created by the withdrawal of Temik from the market.
Our objectives were to: 1) develop and screen thrips tolerant cotton germplasm, 2) map and develop PCR based linked markers for thrips tolerance in upland cotton, and 3) transfer of thrips tolerance into adapted lines. Coastland 320 (Gossypium barbadense) was used as the source of thrips tolerance based on previous work by Bowman and McCarty (1997). Segregating populations from a cross of thrips tolerant Coastland 320 and three upland cotton cultivars were screened each year at the Border Belt Research Station near Whiteville, NC and at the Central Crops Research Station near Clayton, NC. The material was planted in a field where wheat was grown. As the wheat matured, the thrips were expected to leave the wheat and attack the cotton. Four weeks after planting, the susceptible genotypes were rouged out. Susceptible plants show symptoms of thrips damage such as dog-eared cotyledons and first-true leaves. The remaining plants were allowed to intercross. In the fall 2010, single bolls from desirable plants were harvested. The resulting plant material was selfed to obtain F4 homozygous lines. Thrips screening was based a scale of 1 through 5 In the summer of 2011 in the above plant material along with 89 day length insensitive land races of cotton were planted in a wheat field at Clayton, NC. The field was divided into blocks of ten rows of cotton separated by 16 feet of standing wheat to achieve high and uniform thrips infestation on cotton seedlings. Six thrips tolerant families have been identified at Clayton, NC.
Based on the 2011 thrips screening data, individual resistant and susceptible plants were harvested. Selfed bolls from single plants were processed. A total of 280 F5 lines and parents obtained from 2011 harvest and 96 lines of converted race stocks were selected for thrips tolerance screening at central crops research station, Clayton. These lines were planted in a wheat field alternating with strips of standing wheat. Planting was done on April 15th, 2012 as suggested in the cotton producer's meeting. However, because of low and freezing temperatures 5 days after planting cotton germination was severely affected and germination percentage in this field was less than 25%. Germinated plants showed slower growth and discoloration of leaves. In the surviving plants, because of confounding effects of cold damage, phenotyping for thrips tolerance was not successful. Nevertheless the surviving cotton plants were selfed. These, along with the remnant seed of 2011, will be used for thrips screening in summer 2013.
For genetically mapping of thrips tolerance, the original donor introgression line Coastland 320 was used as a male parent in crosses with susceptible cotton lines (Acala Maxxa, TM1, FM966) at Clayton, NC. F1s along with the parents were planted in the summer nursery at Clayton, NC for selfing the F1s and backcrossing to the susceptible parents. F2 population obtained from one F1 combination (FM966 X Coastland 320) selfed at Tecoman, Mexico was planted in the summer nursery to obtain F2:3 populations. Parents used for developing mapping populations are currently being genotyped using SSR markers. F1s of three combinations (FM966 X Coastland 320, GA King X Coastland 320 and Acala Maxxa X Coastland 320) were produced in the greenhouse in spring-2012. These F1s were backcrossed to their respective susceptible recurrent parents FM966, GA King and Acala Maxxa) in summer 2012. These backcross F1s will be screened for thrips tolerance in the summer 2013 as described above sections and tolerant plants will be further backcrossed to susceptible recurrent parents to transfer the thrips tolerance into upland cotton background.
This project fully supports the graduate research assistantship to Ph.D student Ms. Baljinder Kaur. She is screening the germplasm for sources of thrips tolerance, developing techniques for thrips reaction, developing appropriate mapping and segregating populations, and characterizing the thrips tolerance using molecular tools.
|Project Year: 2012|
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