Genetic Analysis of Verticillium Wilt Resistance in Biotech Cotton

Cotton (Gossypium spp.) is considered to be the most cultivated fiber crop worldwide. Two cotton species are currently being cultivated for this purpose: G. hirsutum L. which supplies 90% to world cotton production and G. barbadense that accounts for just 9% of world production. However, diseases cause limiting effects on cotton production. One of the most prevalent diseases in the Cotton Belt of USA and New Mexico is Verticillium wilt (VW). Caused by the the fungus Verticillium dahlia Kleb., it significantly reduces fiber quality and therefore poses a threat to the cotton industry as a whole. The development of VW-resistant cultivars is seen as the most efficient solution to losses in yield. However, existing commercial strains offer only moderate resistance to VW. As a contribution to current efforts, a recent study used quantitative trait loci analysis to determine the heritability of VW resistance, locate the possible position of the resistance genes on the chromosomes and identify molecular markers associated with these genes.

VW-susceptible (upland cotton genetic standard, TM-1) and VW-resistant (introgression upland cotton line NM-24016) were first crossed to produce a recombinant inbred line (RIL). These RILs were inoculated with a defoliating pathotype (BC strain) of V. dahlia and evaluated for VW resistance following a disease rating system (ranging from 0-5). The scoring system was based on the percentage of chlorotic or necrotic leaves, and the number of abscised leaves or cotyledons. These characteristics were determined at specific days after inoculation (DAI). Observations for each DAI were analyzed as separate traits. Genomic DNA was also extracted from 94 RILs for subsequent amplification using 114 RGA-AFLP markers. These marker loci were combined with 990 SSR (Simple sequence repeats) and SNP (Single nucleotide polymorphisms) marker loci to construct a linkage map.

Their results show low to moderate heritability which suggests that VW resistance in cotton is indeed controlled by genes but are also largely affected by the environment.

Read the abstract at http://link.springer.com/content/pdf/10.1007/s11032-013-9987-9.pdf.