Severity of Verticillium Wilt, Plant Growth, and Spectral Reflectance Indices of Chile Pepper Under Periodic Flooding and No-flooding Conditions

Verticillium wilt, caused by Verticillium dahliae, is an economically important disease on chile pepper (Capsicum annuum L.), which is grown primarily under furrow and drip irrigation in New Mexico. Field observations by producers indicate that Verticillium wilt is more prevalent on chile pepper grown under drip irrigation than under furrow irrigation. To test these observations, chile pepper plants at the six- to eight-leaf stage inoculated or noninoculated with V. dahliae were subjected to either periodic flooding or no-flooding conditions in the greenhouse. Plants under periodic flooding were subjected to three events of 7 day flooding and two events of no flooding over a period of 5 weeks. Differences among treatments were assessed using disease severity, plant dry weight, and spectral reflectance-based physiological indices such as moisture stress index (MSI), chlorophyll-based difference index, water band index, and photochemical reflectance index (PRI). There was a significant interaction between flooding and inoculation with respect to disease severity (P < 0.003). In plants inoculated with V. dahliae and subjected to periodic flooding, the relative treatment effect (RTE) based on disease severity was increased from 40% to 130% relative to noninoculated plants subjected to no flooding. However, under conditions of no flooding, RTE increased by 200% to 286% when plants were inoculated with V. dahliae relative to noninoculated plants. In general, periodic flooding and inoculation with V. dahliae were accompanied by a decrease in plant dry weight as well as in the level of spectral reflectance-based physiological indices. In noninoculated plants subjected to periodic flooding, plant dry weight was reduced by 45% to 50% relative to noninoculated plants subjected to no flooding. In plants inoculated with V. dahliae and subjected to periodic flooding, reduction in plant dry weight was 46% to 60% relative to noninoculated plants subjected to no flooding. Under conditions of no flooding, plant dry weight was reduced by 33% to 52% when plants were inoculated with V. dahliae relative to noninoculated plants. Of all the spectral reflectance-based physiological indices, PRI was the most affected by flooding and inoculation. For noninoculated plants, the mean area under the curve for PRI (AUC-PRI) was decreased by 90% under periodic flooding relative to no flooding. In plants inoculated with V. dahliae and subjected to periodic flooding, reduction in AUC-PRI was 93% relative to noninoculated plants subjected to no flooding. Under conditions of no flooding, AUC-PRI was reduced by approximately 93% when plants were inoculated with V. dahliae relative to noninoculated plants. These results showed that chile pepper growth and physiology were affected similarly by flooding and inoculation with V. dahliae. However, severity of Verticillium wilt was greater under no-flooding than under periodic flooding conditions.