Effect of flooding on the viability and pathogenicity of sclerotia ofSclerotium rolfsiiin Malaysian soil∗

Abstract

Sclerotial viability of Sclerotium rolfsii, the seedling blight and collar rot pathogen of chilli, decreased rapidly with time of submerging in flooded field soil. Viability was reduced to 10% 9 days after submerging. No reduction was observed in sclerotia submerged in non-sterilized tap water. Loss of viability resulted in complete loss of pathogenicity. Nongerminated sclerotia became soft and broke easily. Maceration of cortical cells was common. A bacteria-like organism was consistently associated with the ruptured and macerated sclerotia. In glasshouse studies, soil flooded at a high temperature decreased the viability of the sclerotia; this was reflected in a reduced incidence of seedling blight and collar rot on chilli seedlings. The incidence of seedling blight was recorded as 43-7% in the non-flooded soil, 10.2% in flooded soil and 12.3% in the planter that had received an application of Brassicol. However, incidence of collar rot was 25.3% and 28.1 % in the flooded and fungicide-amended soils respectively and 58.1% in the non-flooded pots. It is concluded that satisfactory control of seedling blight and collar rot of chilli can be achieved by flooding.

Bacterial populations concomitant with <i>Sclerotium rolfsii</i> sclerotia in flooded soil, as estimated by 16S rRNA gene, PCR-DGGE and sequence analyses

“…Therefore, practical methods are needed to markedly reduce S. rolfsii sclerotial Journal of Applied Biosciences 93:8696 -8712 ISSN 1997-5902 viability and thus promote increases in crop yield. Some methods have been studied: for instance, flooding of sclerotium-infested fields for one month decreased not only disease incidence but also sclerotial germinability (Nakagawa et al, 1994;Tanaka et al, 1994;Sariah & Tanaka, 1995), and a reduction in sclerotial survival under flooded conditions was hypothesized to be associated with invasion and colonization by bacteria-like organisms (Tanaka et al, 1994;Hyakumachi et al, 2014). So far, the structure and succession of bacterial communities concomitant with Sclerotium rolfsii sclerotia from environment with or without flooding are not well understood.…”