Infection of Sorghum Varieties by the Cotton Root -knot Nematode, Meloidogyne incognita

Twentythree varieties of sorghum, Sorghum bicolor, were evaluated for susceptibility to the cotton root -knot nematode, Meloidogyne incognita race 3. Eggs per gram of root were used as a measure of nematode reproduction and host susceptibility. The nematode reproduced on all varieties tested Mean egg counts were lowest on the varieties Northrup King (NK) KS -737, MF.; NK 1580,M; NK Ks -735 M.F.; NK 714Y MF.; NK Lt. Bronze X 609 M; Ciba-NK C -1506, M; and Pioneer 8877, but these varieties are still considered to be hosts capable of sustaining or increasing nematode populations in cotton fields. All varieties were better hosts than cotton. Introduction The cotton root -knot nematode, Meloidogyne incognita race 3 is a wide -spread problem in Arizona including those areas where sorghum is grown in rotation with cotton. Sorghum isa known host of M incognita but susceptibility varies greatly among varieties (McSorley and Gallaher, 1992) and postseason nematode populations fluctuate accordingly. Fortnum and Currin (1988) tested several varieties of sorghum for susceptibility to M incognita and found that, compared to tomato, nematode reproduction was low, results that have been affirmed by Ibrahim et al. (1993). However, recent field trials in Arizona have shown that yield of cotton lint can be increased by pre -plant treatments of Telone when cotton follows sorghum. Therefore, greenhouse trials were conducted to determine the susceptibility of selected sorghum varieties to M incognita race 3. Materials and Methods Seeds of 23 sorghum varieties were sown, 4 seeds to a pot, in 6inch -diameter plastic pots, containing a sterile 3:1 mixture of washed mortar sand and sandy loam. Ten days after sowing, when the seedlings had reached a height of 2 inches, they were inoculated with 4,700 M incognita infective juveniles per pot. Daytime greenhouse temperature was maintained at 28 +4 C and night temperature at 20 +3C. Plants were harvested 80 days after inoculation, the roots gently washed to remove adhering soil, and the nematode eggs extracted in 20 % household bleach. Each variety was replicated three times (three pots) and the experiment was repeated twice.