Abstract
Since 1947, stem rot of peanut caused by a Diplodia has been found in some fields in the Kanto district. The pathogen produces pycnia on the affected stems and petioles. Immature pycniospores are hyaline and 1-celled, while mature spores are dark and 1-2 celled, measuring 19-30 ×10-17μ in size. The perfect stage has not been found on the plants nor in culture. The organism grows well on media of various kinds. The cardinal temperatures are 12-30-31∼40°C. Optimum pH for growth is 4.0-6.1. The cultures isolated from peanut could kill not only peanut but beans. They caused rots of melon, apple, Satsuma orange, corn-ear, and cotton-boll. On adzuki bean (Phaseolus angularis Wight), soybean and sweet potato, they simply produced necrotic lesions.
Morphologically and physiologically the organism resembles closely with each of Diplodia gossypina, D. tubericola, D. natalensis, and D. frumenti, and is believed to be a strain of the collective species including these allied species. It remains the need for further investigation for identification, but the name of D. natalensis was tentatively adopted following Jacoway(6) and Ramsey(11).
