Factors Affecting Growth and Sporulation of A scochyta fabae f. sp. lentis. WALTER J. KAISER, Research Plant Pathologist, USDA-ARS, Western Regional Plant Introduction Station, Washington State University, Pullman 99164-6402. RICHARD M. HANNAN, Research Horticulturist, USDA-ARS, Western Regional Plant Introduction Station, Washington State University, Pullman 99164-6402; and JACK D. ROGERS, Professor, Department of Plant Pathology, Washington State University, Pullman 99164-6430. Plant Dis. 78:374-379. Accept for publication 27 December 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994. DOI: 10.1094/PD-78-0374.

Isolates of Ascochyta fabae f. sp. lentis from seed of lentil (Lens culinaris) collected from different countries varied greatly in growth, sporulation, colony appearance, and morphology. Optimum conidial production occurred on 5% lentil seedmeal agar and natural potato-dextrose agar (PDA), whereas optimum linear growth occurred on natural PDA or oatmeal agar. Optimum temperatures for linear growth and sporulation were 15 20°C and 15-25°C, respectively. Isolates did not sporulate at 30°C. In continuous light, sporulation of all isolates was three to 10 times greater than in darkness, but linear growth in continuous light was greater in only two of three isolates. Zonation (alternation of zones of mycelial and pycnidial production) did not occur in continuous light or continuous dark but was pronounced when some isolates were exposed to alternating light and dark. Conidia usually had one to three septa, but frequency distributions for septation number differed greatly among 13 isolates. The proportion of conidia with one septum ranged from 67 to 95%. Conidia with multiple septa were longer but not wider than conidia with one septum. Conidia with the same number of septa varied little in size, but multiseptate conidia were significantly longer than those with one septum. Conidiogenous cells, which were morphologically simple, lined the pycnidial cavity and proliferated percurrently. Conidia can originate and secede at the same level as, or at a higher or lower level than, the previous conidium. The pathogenicity of 24 isolates of A. f. lentis from 17 countries was tested on two commercial lentil cultivars. All isolates were pathogenic, producing necrotic lesions on leaves, petioles, and stems of inoculated plants.