Effects of wetness duration, inoculum concentration and temperature on the development of Alternaria blight on transplants of sweet potato

Abstract

Alternaria blight (AB) of sweet potato caused by Alternaria bataticola is a limiting factor for sweet potato industries in various countries. The disease has been recently reported in South Africa. Thorough literature search indicates that factors influencing the development of AB have not been studied adequately. In the current study, wetness duration, inoculum concentration and temperature/wetness duration interaction were evaluated for their effects on the disease incidence and disease severity of AB of sweet potato. Cultivars W119 reported susceptible to AB were inoculated with a spore suspension of A. bataticola (PPRI 11930) under glasshouse and plant growth chamber conditions. In the wetness duration experiment at the constant temperature of 28°C each increase of wetness duration significantly increased the mean disease incidence (MDI) and mean disease severity (MDS). Exposure for 48h was the optimum condition of this experiment, as it resulted in the highest MDI and MDS. In the inoculum concentration experiment the MDI and MDS increased significantly as inoculum concentration increased but there was no significant difference between 3x10 4 conidia mL-1 and the highest inoculum concentration of 5x10 4 conidia mL-1. In the interaction of temperature and wetness duration the optimal temperatures and wetness duration in this study were 20 and 25°C for 48 h, respectively. Exposure at 35°C irrespective of wetness duration period did not produce any AB symptoms as shown by the MDI and MDS.

Evaluation of Sweetpotato (Ipomoea batatas (L.) Lam.) Genotypes for Resistance to Alternaria Leaf Petiole and Stem Blight (Alternaria spp.) in Uganda

“…Vloutoglou and Kalogerakis (2000) reported an increase from 2 to 88% leaf area infection by A. solani on tomato (Solanum lycopersicum L.) when the duration of leaf wetness was increased from 4 to 24 hours and no symptoms when wetness was less than 4 hours. Similarly, Kandolo et al (2018) reported temperature range of 20-25°C and wetness duration of 48 hours as the ideal conditions for the spread of Alternaria bataticola. Kachwekano had lower daily temperatures and higher relative humidity than Namulonge, consequently the residual moisture on the plants took longer to evaporate thereby facilitating the infection process.…”

Seventy years of sweet potato [Ipomoea batatas L. (LAM)] research in South Africa

“…Kandolo et al. (2018) found that the ideal conditions for spread of blight are 48 h of wetness and temperatures between 20°C and 25°C. Among the fungicides tested under field conditions, the mixture of azoxystrobin–difenoconazole at 375 mL/100 mL was the most effective in reducing Alternaria leaf and stem blight intensity (Kandolo et al., 2016).…”