Determination of the variability of colletotrichum Truncatum, the causal agent of Anthracnose of Soyabean (Glycine max( L) Merr.) in Zambia
Mayonjo, David Onesmo
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Soyabean (Glycine max (L) Merr.) has become an important crop in Zambia. Its increased production is hampered by several foliar diseases of which the anthracnose caused by Collectotrichum truncatum appear to be the most prevalent, than red leaf blotch cause by Dactuliochaeta glycines reported before. A study on anthracnose of soyabean disease was undertaken to determine the level of variability that exists in the pathogen populations in Zambia. Ten samples of anthracnose of soyabean were collected from the provinces of Central, Lusaka and Southern. Isolates Ct-01, Ct-02,and Ct-03 were collected from Central province (Kabwe); Ct-04, Ct-05, Ct-06, and Ct-07 from Lusaka province ( Lusaka-West and South), and Ct-08, Ct-09, and Ct-10 from Southern province (Mazabuka). Isolation were made following conventional mycological methods and the identification was confirmed by the International Mycological Institute, England. Isolates were characterized on the basis of acervulus size, colony features and its growth rate on potato Dextrose Agar (PDA) and Malt Extract Agar (MEA). The conidial size , germ tube elongation during conidial germination and pathogenicity of the isolates to three soyabean cultivars were also determined. The isolate Ct-07 had the largest acervulus diameter and Ct-03 had the lowest. After eight days of growth, Ct-04, Ct-05, Ct-07, and Ct-09 had greater colony diameter on PDA whereas these isolates produced significantly smaller colonies on MEA. In comparison, Ct-01, Ct-03, Ct-06, and Ct-08 had reduced growth rate and produced smaller colonies on PDA. After eight hours of growth on water agar, isolates Ct-04 and Ct-09 developed the longest germ tubes as compared to Ct-06 and Ct-08. Conidial size also showed significant differences among isolates. Differences in colour of conidial ooze emanating from the acervulus and the colony margin were also noticed among isolates at 25 degrees Celsius. The colour of aerial hyphae showed differences on the two media, but the majority of the isolates produced white hyphae which later turned grey.The isolates differed in ther ability to infect soyabean cultivars. Isolates Ct-01, Ct-07 and Ct-09 infected kaleya, Hernon-147 and Santa Rosa the tested cultivars whereas Ct-02, ct-04, and ct-08 infected only kaleya and Hernon-147. Isolates Ct-05 and Ct-10 attcked only kaleya and Santa Rosa and Isolates Ct-03 and Ct-06 infected only Kaleya and Santa Rosa respectively. The resullts indicate that the ten isolates of Colletotrichum truncatum posses considerable morphological and physiological variability and therefore their control measures should be directed after knowing which one of the trains of the pathogen is in the population.
- Agricultural Sciences