Effects of temperatures on survival of Aphelenchoides besseyi in prolonged storage of rice grains

Abstract

Summary The white-tip nematode, Aphelenchoides besseyi, is a seed-borne ectoparasite of the rice plant Oryza sativa. Nematodes in dried rice seeds are in dehydrated quiescence or anhydrobiosis and are reactivated by rehydration. To understand the persistent parasitism better, the effects of temperature on nematode survival were examined during prolonged periods of seed storage. There was a marked difference in the survival rate among different temperatures; survival was lower at 20 and 25°C than at −5 to 10°C after storage for 190 days. No nematodes survived a storage period of 1313 days at 20 and 25°C. When rice seeds were held at 5°C, the survival rate of nematodes decreased during a period of 7315 days. The estimated instantaneous rate of mortality per month was higher in the early and late parts of the period than in the middle part. Another nematode population also showed a reduction in the survival rate during 6553 days storage at 5°C. In storage at −30°C, survival was not affected during a period of 6485 days. After storage at −30°C for 6546 days, 96% of rice seeds germinated, whereas 60-96% of seeds of two groups germinated after storage at 5°C for 6610-7373 days. Therefore, prolonged storage of rice seeds at 5 or −30°C was unlikely to disrupt the connection between rice plants and A. besseyi.

An emergent plant‐parasitic nematode in Brazil: Aphelenchoides besseyi. Current status and research perspectives

“…A. besseyi has an outstanding ability to survive in anhydrobiosis for several years on stored rice grain (Hoshino & Togashi, 2020;Wang et al, 2014) important to find the causal agent of GSFR (Chaves et al, 2013;Meyer, Favoreto, Klepker, et al, 2017). This undoubtedly raised awareness of the nematode, and losses in cotton were published in 2018 .…”

“…Interestingly, it has been reported that nematodes reach upper parts of the plant by moving ectoparasitically in some crops (e.g., rice and common bean; Araya, 2008; De Jesus & Cares, 2016; Hoshino & Togashi, 2020), while endoparasitically, through the cortical cells, on others (e.g., soybean; Calandrelli et al., 2023; Favoreto & Meyer, 2019). Experimental evidence showed that migratory stages penetrate soybean roots and hypocotyls (Calandrelli et al., 2023; Da Silva & Machado, 2022).…”

“…As a seed‐transmitted nematode, A . besseyi has an outstanding ability to survive in anhydrobiosis for several years on stored rice grain (Hoshino & Togashi, 2020; Wang et al., 2014). Therefore, it is reasonable to postulate that this could have been a key factor in the dissemination of A .…”

Sex ratio of Aphelenchoides besseyi within Oryza sativa seeds with relation to reproduction of rehydrated adult females

“…After harvesting, the fourth‐stage juveniles and adults are dehydrated, coiled and motionless under the hulls of dried rice seeds (Hoshino & Togashi, 2020; Huang & Huang, 1972, 1974). Taking account of the water content of seeds (15%) after the postharvest desiccation (Hoshikawa, 1989), the nematodes are considered to be in a dehydrated quiescent state (quiescence in the hypometabolic state) rather than “cryptobiosis” in the undetectable levels of ametabolism (Hoshino & Togashi, 2020; Rao, 2018; Watanabe, 2006). When soaking the dried seeds in water, the nematodes revive, come out of the seeds after germination and infect the rice seedlings (Tamura & Kegasawa, 1957).…”

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The white-tip nematode, Aphelenchoides besseyi, is a seedborne ectoparasite of rice, Oryza sativa (Fukano, 1962;Todd & Atkins, 1958).The nematode reproduces in cavities above the growing tip of the rudimentary culm, on the young leaf surrounded by the innermost leaf sheath during the tillering stage, and in the florets and immature seeds (Goto & Fukatsu, 1952;. After harvesting, the fourth-stage juveniles and adults are dehydrated, coiled and motionless under the hulls of dried rice seeds (Hoshino & Togashi, 2020;, 1974. Taking account of the water content of seeds (15%) after the postharvest desiccation (Hoshikawa, 1989), the nematodes are considered to be in a dehydrated quiescent state (quiescence in the hypometabolic state) rather than "cryptobiosis" in the undetectable levels of ametabolism (Hoshino & Togashi, 2020;Rao, 2018;Watanabe, 2006).

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