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.