Crude toxin production and chemical control of Boeremia exigua.

Mung bean (Vigna radiata (L.) R. Wilczek) rotiform disease is caused by Boeremia exigua var. exigua which affects seriously its yields and quality. During its growth, B. exigua can produce toxins but less is known about it. The biological characters of B. exigua were studied. The ideal culture conditions of mycelial growth were pH 5-8, 25 °C, static, and continuous light for 27 days, mannitol can replace sucrose as the most favorable carbon source in the modified Czapek solution, moreover, the addition of inositol or Vitamin B2 was benefit. The ideal culture conditions of crude toxin production were pH 5-7, 25 °C, static, and continuous light for 21 days, the studies did demonstrate that Czapek medium resulted in high levels of toxin formation, while Malt extract and Richard medium resulted in low production levels of toxins, there were no toxins are produced in PD medium at all. Sucrose and glucose can be used as suitable carbon source for the production of toxins, moreover, the addition of inositol or Vitamin C can stimulate the crude toxin production of B. exigua. The crude toxin of B. exigua has good thermal stability, low sensitivity to various wavelengths of light. It is also shown that crude toxins could inhibit the germination and radicle elongation of mung bean, lead to necrotic spots on leaves and have a strong wilt effect on seedlings of mung bean. It also had different degrees of inhibition to other crops such as sorghum, string bean and so on. In order to better control the disease, laboratory toxicities of 21 fungicides were tested. it revealed that Prochlomz has the greatest inhibitory effect, followed by Prochlomz and Carbendazim.