Effect of enhanced UV-B radiation on reniform nematode (Rotylenchus reniformis Linford and Oliveira) populations in cotton (Gossypium hirsutum L.)

To understand the effects of increased UV-B radiation on reniform nematode (Rotylenchus reniformis Linford and Oliveira) populations, cotton (Gossypium hirsutum L.) plants were exposed to three levels of UV-B radiation [0 (control), 6 and 12 kJ m^-2 day^-1] in a glasshouse from emergence to early square stage. At each UV-B treatment four populations [0 (N₀), 2500 (N₂₅₀₀), 5000 (N₅₀₀₀) and 7500 (N₇₅₀₀)] of reniform nematodes were incorporated into the sterilized rooting medium. Plant growth, development, photosynthetic parameters, pigments, phenolics and the number of eggs and nematode numbers in the rooting medium were recorded at the end of the experiment 40 DAS. Even though, UV-B radiation did not significantly affect plant growth and development it did significantly increase leaf and root phenolic concentrations. UV-B treatments significantly decreased both the egg and nematode numbers in all the nematode population treatments. Significant negative correlation was found between cotton leaf phenolic concentration and egg (slope = -69.4; R² = 0.72) and nematode (slope = 103; R ² = 0.53) numbers. Similarly, root phenolics also showed negative correlation with egg (slope = -3184; R² = 0.26) and nematode numbers (slope = -5857; R² = 0.30). Therefore, current and projected UV-B radiation levels may have an important regulatory influence on nematode populations.