Infection Biology of Bipolaris oryzae in Rice and Defence Responses in Compatible and Less Compatible Interactions

Abstract

The infection biology of Bipolaris oryzae and the defence responses of its host rice were studied using the rice cv. MTL 189 inoculated with two isolates of B5 (highly compatible with MTL 189) and K2 (less compatible). In the former interaction, the hyphal progress was accompanied by tissue degradation and extensive sporulation after 8 days, whereas in the latter interaction, only very limited tissue degradation and sporulation was observed. Quantitative microscopy of the infection showed that the percentages of conidia and appressoria causing penetration and fluorescent epidermal cells (FEC) were lower for isolate K2 than for isolate B5 at 12 and 24 hours after inoculation (hai). Fluorescent papillae (FP) were only seen in the less compatible interaction and the percentage of conidia causing single FEC was highest in the less compatible interaction at 12 hai, but not at 24 hai. Qualitative examination of other defence responses showed that H2O2 started to accumulate at 4 hai in the less compatible interaction, whereas it appeared in the compatible interaction only at 12 hai. The level of H2O2 was generally higher in the less compatible than in the compatible interaction. Cross sections of leaves showed that H2O2 accumulated in the outer walls of epidermal cells. Likewise, accumulation of callose and polyphenolic substances was most pronounced in the less compatible interaction and occurred at the same places as H2O2. To our knowledge, this is the first report implicating H2O2 as an early defence response against the hemibiotrophic pathogen B. oryzae during early infection stages in rice. Understanding defence reactions may aid in resistance breeding.

Mycoflora associated with stored rice from storage facilities in Makassar and Maros, Indonesia

“…Rhizoctonia solani can survive for extended periods in the soil, and infected plant debris or soil particles can adhere to the surface of seeds, potentially leading to transmission during planting or germination (Singh et al 2019). Bipolaris oryzae is a seedborne pathogen known as the causal agent of brown spots in rice; it is a hemibiotrophic parasite that can infect and remain dormant in the seeds, and the dormant inoculum will be reactive during seed germination (Sunder et al 2014;Ackaah et al 2023;Thuy et al 2023). So far, there is no report of mycotoxin produced by these pathogens or any other risk related to human health.…”

Infection Biology of Stagonosporopsis cucurbitacearum in Watermelon and Defence Responses in the Host

“…H 2 O 2 is a relatively stable reactive oxygen species, produced by many plants as a response to pathogen attack [36]. The role of H 2 O 2 in defence has been reported from many host-pathogen interactions [23,30,35,[37][38][39]. H 2 O 2 produced at the penetration sites can directly inhibit pathogen penetration [23,24,30,37,39].…”

“…The role of H 2 O 2 in defence has been reported from many host-pathogen interactions [23,30,35,[37][38][39]. H 2 O 2 produced at the penetration sites can directly inhibit pathogen penetration [23,24,30,37,39]. In addition, H 2 O 2 participates in oxidative cross-linking of proteins in the cell walls, lignification and furthermore, H 2 O 2 may also serve as a signalling compound activating defence responses [32,35,40].…”

“…Data from studies of infection biology and H 2 O 2 accumulation represent discrete variables and were therefore assumed to follow a binomial distribution. They were analysed by logistic regression as described previously [23,30]. Data for leaf infection, length of stem lesions and enzyme activities represent continuous variables and were analysed by analysis of variance assuming a normal distribution.…”

Influence of production situation on the incidence of brown spot of rice (Oryza sativa) caused by Bipolaris oryzae in the Philippines

“…The same mechanism governs the reported high amount of BS even in irrigated areas with reduced water supply (Savary et al., 2005, 2022). Another explanation for the development of BS in rainfed areas is that the pathogen enters the plant through the epidermis (Thuy et al., 2023) instead of the stomata. The pathogen can still enter the plant tissues despite the closure of stomata that occurs in plants, including rice, as an adaptation to prevent water loss under water‐stressed conditions (O'Toole & Cruz, 1980).…”