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Description:
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Whiteflies (Bemisia tabaci , Biotype B , Homoptera : Aleyrodidae ) are pests of cotton crops , affecting the yield of the crop both indirectly and directly . These pests feed on the leaves of cotton plants and produce "honeydew ," a sticky liquid excretion which covers the lint of the open cotton boll creating problems during the processing of the lint . High densities of these pests also can decrease the productivity of the cotton plant by stripping it of vital nutrients . The primary objective of this research was to screen 116 converted cotton race stocks for resistance to sweetpotato whiteflies . Responses of converted race stocks to whiteflies are compared to that of known susceptible commercial cultivars PSC 355 and Delta Pearl .
Screens for antibiosis resistance to whitefly were established using excised leaves placed in a nutrient solution (¼ strength Hoagland's ) . Cohort populations of whiteflies were established on these leaves and followed daily to determine differences in developmental time as well as percent survival . Resistant candidates were determined using a chi -squared test comparing the ranked sums of leaf averages for the two selection criteria , whitefly developmental time and percent whitefly survival , of each cotton race stock to that of the putative known susceptibles (KS ) . These tests showed 6 converted race stocks to be significantly different (P ≤ 0 .1 ) from the KS for at least one of the two selection criteria . Of these converted race stocks , M -9044 -0154 and M -9044 -0156 showed to have lower whitefly survival than the KS , while M -9644 -0188 , M -9644 -0195 , M -0044 -0221 , and M -9644 -0242 showed whitefly to have an increased developmental time . Retesting of these six converted race stocks along with several others identified another race stock line , M -0044 -0171 , which was significantly different from the KS . Retesting also indicated that M -9644 -0188 was different for survival in addition to developmental time which was determined in the original screening .
Additional tests were conducted in the greenhouse and field to examine these race stock lines . Greenhouse screenings indicated that M -9044 -0156 and M -9644 -0188 contained possible non -preference resistance characteristics . Field screenings conducted in Weslaco and College Station , TX in 2002 and 2003 failed to provide useful data due to low densities of insects . |