DIDYMELLA-EXITIALIS ON WHEAT IN NEW-ZEALAND

Didymella exitialis (Morini) Muller was identified on wheat (Triticum aestivum L.) leaves collected during a survey of New Zealand wheat cro ps in the 1990/91 season. This fungus was identified on nine cultivars in the major wheat-growing areas and was present in 19 out of 42 crop s surveyed. In the 1992/93 season, D. exitialis pseudothecia first occ urred in late November and became increasingly common as leaves and cr ops senesced. The teleomorph was more common than the Ascochyta anamor ph. Pseudothecia of D. exitialis were frequently associated with leaf scorch symptoms, but were also often abundant over the surface of sene sced leaves. The elongate lesions were tan to dark brown in the centre with diffuse margins. Thirty-two single ascospore isolates were made. Cultures sporulated sparsely on potato dextrose agar under near-UV li ght, producing the Ascochyta anamorph. Inoculation of wheat plants usi ng pycnidiospores from culture resulted in disease symptoms, mostly on the margins and tips of leaves, after c. 2 weeks. Pseudothecia develo ped c. 2 weeks later and D. exitialis was re-isolated from infected le aves. Large differences in the leaf area covered with D. exitialis wer e found between cultivars in three field trials. 'Otane' and 'Norseman ' were severely affected in all trials, whereas 'Monad' and 'Kokako' w ere almost unaffected. Didymella exitialis has not previously been rec orded on wheat in New Zealand.