棉铃疫菌的越冬存活

OVERWINTERING AND SURVIVAL OF PHYTOPHTHORA BOEHMERIAE IN COTTON BOLL RESIDUE IN THE SOIL

用MTT活体染色法,对棉铃疫苗(Phytophthora boehmeriae Sawada)的存活越冬进行了研究,结果表明:孢子囊和卵孢子均可在棉田土中的病残体(烂钤壳,棉籽)上存活。其中孢子囊可存活3～4个月,且其存活率可高达58.0％,认为孢子囊在棉铃疫病的再侵染过程中起重要作用。但孢子囊在1月份温度达零度时就全部死亡,不能越冬。而卵孢子在历经1990年至1991年冬季零度以下76天(其中最低温度达—2.8℃)后仍可以存活,在存活300天以后其存活率达48.8％,证明卵孢子是毫无疑问的越冬菌态。生物测定,越冬后卵孢子形态观察,卵孢子萌动变化与温度的关系表明,越冬存活的卵孢子可以成为棉铃疫病的初侵染来源。

Field tests of studying the overwintering and survival of Phytophthora boehmeriae Sawada by means of a vital stain MTT(tetrazolium bromide) were carried out in Hebei Province. The results showed that both sporangia and oospores could survive in the boll residues in the soil. The survival period of sporangia in the soil was about 3--4 months and the percentage of survival was 58. 0%. Therefore they must play a major role in the infection cycles to cotton bolls. However, the viability of sporangia were considerably effected by low temperature and no viable sporangia were observed at 0 C in January. The oospores were confirmed to be the overwintering propagules of P. boehmeriae and survived at least 300 days from 1990 to 1991 with 76 days below 0℃ (the lowest one was -2. 8℃). The final survival rate was 48. 8%. Bioassays and morphological observations of the overwintered oospores on cotton boll residue, and the relationship between the oospores inactivating rate and temperature revealed that the overwintered oospores were the source of the primary infection of cotton boll blight.