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New technique evaluates cotton variety performance under Verticillium wilt conditions in High Plains

Verticillium wilt hits producers in the pocketbook every year on the Texas High Plains, and is the number one yield-reducing disease in the area.

“Since 2004, Verticillium wilt has been the most important disease of cotton, even surpassing nematode damage most years,” said Terry Wheeler, plant pathologist with the Texas Agricultural Experiment Station at Lubbock.

Wheeler and associates test numerous cotton varieties for Verticillium wilt tolerance each year at several High Plains locations across northern, central, and southern sections of the High Plains.

“Because new cotton varieties are marketed each year, and older varieties are dropped, it is difficult to get long-time performance records for any given variety,” Wheeler said. “So we devised a technique which combines data from two or more 2006 and 2007 Verticillium wilt-infected sites into a single relative value for each of 59 varieties.

“Variety characteristics used in the analyses include lint yield, value per acre, and wilt infestations. These values can be very useful to producers in deciding which varieties they need to plant in Verticillium wilt-infected fields.”

Relative yield values within each test site were obtained by dividing the lint yield of each variety by the highest lint yield obtained within that particular site. These individual values for each variety were then statistically averaged across all sites (in which that cultivar had been tested) to get an overall relative yield for each variety.

The relative values per acre were obtained by multiplying the yield per acre by the appropriate loan value, then subtracting the seed costs and the technical fees.

Relative wilt values for each test site were obtained by dividing the wilt incidence of each variety by the highest wilt incidence for the site.

The overall relative value per acre and the overall relative wilt values were obtained by the same technique used to obtain overall relative yields.

The top 10 varieties and their overall relative yield value were:

· Deltapine 455 BG/RR) (0.94),

· FiberMax 960BR (0.94),

· FiberMax 9058RF (0.90),

· NexGen 2448R (0.89),

· FiberMax 960B2R (0.89),

· FiberMax 9150RF (0.89),

· FiberMax 9180B2RF (0.88),

· Paymaster 2326RR (0.88),

· FiberMax 989BR, (0.88), and

· FiberMax 9060RF (0.87)

Overall relative values per acre for the top 10 varieties were:

· NexGen 2448R (0.95),

· FiberMax 960BR (0.91),

· Deltapine 455 BG/RR (0.90),

· Paymaster 2326RR (0.90),

· FiberMax 960B2R (0.86),

· FiberMax 9058RF (0.86),

· FiberMax 9180B2RF (0.85),

· FiberMax 9150RF (0.84),

· FiberMax 9063B2RF (0.83), and

· FiberMax 989B2R (0.82)

“The top eight varieties for overall relative lint yields were also the top eight varieties for value per acre,” Wheeler said. “And there were no significant differences among these varieties for either overall relative lint yield or overall relative value per acre.”

The 10 varieties having the lowest overall relative wilt values were:

· Paymaster 2326RR (0.28),

· FiberMax 1880B2RF (0.37),

· FiberMax 1840B2RF (0.37),

· AFD 5064F (0.42),

· AFD 5065B2F (0.42),

· Stoneville 4427B2RF (0.43),

· CS 370001G (0.44);

· NexGen 2448R (0.45),

· FiberMax 989BR (0.48),

· Paymaster 2140B2RF (0.49)

(Note: CS 370001G is a combination of varieties DynaGro 2100B2RF, Cropland Genetics 3020B2RF and Beltwide 3255B2RF under the Cotton States designation.)

“Generally we expect varieties with the higher wilt readings to be among the varieties lowest in yield. However, an examination of the data revealed some varieties had excellent overall relative values for yield even though their tolerance to wilt was quite low. Examples of this include Deltapine 455 BG/RR and FiberMax 960BR, the two top yielders. Their overall relative wilt values were 0.62 and 0.56, respectively,” Wheeler said.

“The Roundup Ready Flex varieties that were ranked in the top 20 percent in value per acre — FiberMax 9058RF, FiberMax 9150RF, FiberMax 9180B2RF, FiberMax 9063B2RF, and FiberMax 9060RF — averaged 0.72 relative wilt ratings. The older picker varieties that were recommended in previous years — Deltapine 455 BG/RR, FiberMax 960BR, FiberMax 960B2R, FiberMax 989BR, and FiberMax 989B2R — averaged relative wilt ratings of 0.55.

“So, the newest Roundup Ready Flex varieties are prone to worse Verticillium wilt incidence than previously recommended varieties. It is unknown whether this will lead ultimately to less stability in performance in particularly bad wilt years, or higher population densities of Verticillium wilt in the soil than under the older Roundup Ready varieties,” Wheeler said.

The rankings for overall relative lint yield, overall relative value per acre, and overall relative Verticillium wilt tolerance for all 59 varieties will be available in Effect of Verticillium wilt on cotton varieties in 2007 and posted on the Web site in February.

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