Cotton Host Plant Resistance To Silverleaf Whitefly Is Discovered

The Issue

Cotton Host Plant Resistance To Silverleaf Whitefly Is Discovered
Foreground: little whitefly damage to okra-leaf cotton. Background: whitefly damaged cotton varieties.
Since 1991, Silverleaf whitefly, Bemisia argentifolii, has caused severe economic losses to cotton and other crops in California and the US. In 1996, 554,215 acres of cotton were reported to be infested in Arizona and California. Lint losses were estimated at 24,891 bales, resulting from reduced yield and contamination of lint with honeydew and sooty molds. Cotton leaf crumple disease, transmitted by the whitefly and caused by cotton leaf crumple geminivirus (CLCV), can also cause extensive reduction in yield.

What Has ANR Done?

Host plant resistance offered one possible alternative for whitefly control in cotton. UCCE test results showed significant differences among cotton varieties and breeding lines for whitefly infestation levels. Two resistance mechanisms were discovered, smooth leaf cotton and okra-leaf shape cotton.

Smooth leaf cotton supported fewer whiteflies than hairy leaf cotton. Leaf hairiness is associated with increased boundary layer humidity on leaf surfaces. Extremely high air temperatures, low relative humidity, and limited irrigation in the desert southwest may result in subtle changes in underleaf humidity influencing Bemisia egg and nymph survival.

Okra-leaf cotton had fewer whitefly adults, eggs and nymphs than normal-leaf cotton. The okra-leaf characteristic may provide higher ambient temperature and lower humidity in the cotton canopy, creating a micro-climate unfavorable to whitefly survival.

The Payoff

Whitefly-resistant cotton varieties reduce insecticide usage

Host plant resistance to whiteflies is clearly offering an economical and non-polluting alternative to whitefly management in cotton. Planting of the cotton varieties DP 5415 and NuCotn 33B, which are less susceptible to infestation by silverleaf whitefly, contributed to a reduction in insecticide use on cotton in Southern California since the early l990s. FiberMax okra-leaf cotton varieties with some whitefly resistance are now being marketed in the US and California, giving growers an additional whitefly management option.

Contact

Supporting Unit: Imperial County

Eric T. Natwick, UC Cooperative Extension
UC Desert Research & Extension Center
1050 East Holton Road, Holtville, CA 92250-9615
760) 352-9474 (Voice) (760) 352-0846 (Fax)