Ascochyta spp. (teleomorphs: Didymella spp.) infect a number of legumes, including many economically important species, and the diseases they cause represent serious limitations of legume production worldwide. Ascochyta rabiei, A. fabae, A. pisi, A. lentis, and A. viciae-villosae are pathogens of chickpea (Cicer arietinum), faba bean (Vicia faba), pea (Pisum sativum), lentil (Lens culinaris), and hairy vetch (V. villosa), respectively. Inoculations in the greenhouse and in growth chambers demonstrated that A. fabae, A. lentis, A. pisi, A. rabiei, and A. viciae-villosae were host specific. Isolates caused no visible disease symptoms on "nonhost" plants (plants other than the hosts they were originally isolated from) but were recovered consistently from inoculated, surface-disinfested, nonhost tissues. Interspecific crosses of A. pisi x A. fabae and A. viciae-villosae x A. lentis produced pseudothecia with viable ascospores, and the hybrid status of the ascospore progeny was verified by the segregation of mating type and amplified fragment length polymorphism (AFLP) markers. Interspecific progeny were morphologically normal in culture but exhibited more phenotypic variation compared with progeny from intraspecific crosses. Mating type and the majority of AFLP markers segregated in Mendelian 1:1 ratios in both intraspecific and interspecific crosses. A total of 11 and 7% of AFLP markers showed segregation distortion among progeny from interspecific crosses and intraspecific crosses, respectively; however, this difference was not significant (P = 0.90). Only 30 of 114 progeny isolates from the A. fabae x A. pisi cross inoculated in the greenhouse caused lesions on pea and only 4 caused disease on faba bean. In all, 15 of 110 progeny isolates were pathogenic to pea and none were pathogenic to faba bean under growth chamber conditions. Although no obvious postzygotic, intrinsic isolating barriers were identified in any of the interspecific crosses, it appears that host specialization may act as both a prezygotic, ecological isolating barrier and a postzygotic, extrinsic, ecological isolating barrier in these fungi. Host specificity, coupled with low pathogenic fitness of hybrids, may be an important speciation mechanism contributing to the maintenance of hostspecific, phylogenetic lineages of these fungi.

Fungi colonizing senescent chickpea (Cicer arietinum) stems and postharvest debris from Pullman, WA, were enumerated and identified with the objective of finding species potentially useful for biological control of Didymella rabiei (conidial state ¼ Ascochyta rabiei), causal agent of Ascochyta blight. In addition to D. rabiei, primary colonizers were, in order of decreasing abundance, Alternaria tenuissima, Al. infectoria, Ulocladium consortiale, Epicoccum purpurascens, U. atrum and Fusarium pseudograminearum. Present at lower frequencies were Al. malorum, Cladosporium herbarum, Aureobasidium pullulans, Clonostachys rosea and miscellaneous anamorphic ascomycetes. On agar media and autoclaved chickpea stems, Au. pullulans consistently grew faster than As. rabiei, and excluded As. rabiei from the substrate. When stems received prior inoculation with Au. pullulans or Cl. rosea, followed by inoculation with compatible mating types of D. rabiei, formation of pseudothecia and pycnidia of D. rabiei was suppressed. Results suggest that Au. pullulans and Cl. rosea can inhibit As. rabiei and its sexual stage, D. rabiei, on chickpea debris. Clonostachys rosea formed appressoria on, then invaded, hyphae of D. rabiei. Small-scale field experiments using Au. pullulans and Cl. rosea have been initiated.www.blackwell-synergy.com