Abstract
Web-blotch, a new peanut disease in Texas, was caused by Mycosphaerella argentinensis. Sexual and asexual reproductive structures of the fungus were produced under natural conditions but only pycnidia were produced on agar media. Maximum fungal growth on malt extract agar (MEA) was at 20 , with no growth at 35 C. Reproduction on sterilized leaves was greatest at 20 C. Pseudothecia were produced at 15 and 20 C but not at 25 C. Pycnidia formed from 10 to 30 C, the extremes tested. The fungus was homothallic and required light for reproduction. Conidia produced on MEA were predominantly one-celled (ca 6 x 3 u) while most of those produced on decaying leaves had one spectrum and were much larger (ca 15 x 5 U). Temperature only slightly affected spore size and septation. Conidia and ascospores germinated and penetrated peanut leaves in a similar manner. Penetration was direct but was followed by subcuticular growth instead of immediate penetration of the epidermis. The epidermal penetration occurred, it was intercellular. Rapid cellular death did not result from invading hyphae. Stems and petioles were susceptible to infection but much less than leaves. Adaxial leaf surfaces were infected more than abaxial surfaces. Symptoms, in growth chamber experiments, were visible four days after inoculation. Blotch symptoms were most common under field conditions but they did not develop on plants artificially inoculated. Temperature and humidity changes in growth chambers did not affect the occurrence of web and blotch symptoms. Virginia-type peanut cultivars were not as susceptible as Spanish-types. The resistant types did not exhibit a hypersensitive response but rather exhibited a limitation in disease development. Blotch size was not restricted on the less susceptible cultivars. Selection for a more pathogenic race was not evident. Six legume genera were hosts of M. argentinensis. The most susceptible were sweetclover and hairy vetch. Symptoms on these hosts consisted of necrotic spots which were not like the web blotch symptoms on peanuts. No host beside peanut was found under natural conditions.
Philley, George Loyd (1975). Peanut web-blotch: growth, pathogenesis and hosts of the causal agent, Mycosphaerella argentinensis. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -184146.