A late frost occurred in the Southland region of New Zealand in November 1995 when many winter wheat (Triticum aestivum L.) crops were at early grain fill, and resulted in a large number of insurance claims for frost damage. In this study, frost damage was characterised. Spikes in affected crops were sharply tapered from a point half to two-thirds from their bases. Grains were as much as 80% lighter in upper parts of affected spikes. Overall yield losses as a result of frost of between 13 and 33% were calculated in affected crops. Grains were sectioned and examined with a scanning electron microscope. Whereas in healthy grains, the layers making up the pericarp and testa were compressed, in frosted grains these layers comprised loosely compressed and unstructured networks of cells. The aleurone layer was less ordered in frosted than in normal grains, and was not always readily distinguished from the starchy endosperm. Rehydration of frosted grains was accompanied by expansion of pericarp and testa cells, whereas little cell expansion occurred in normal grains. Blisters were common in frosted grains, where the outer layers were detached from the remainder of the pericarp.
Surveys for virus disease in potato {Solanum tuberosum L.) ware crops were completed over three successive seasons. Overall mean incidence of viruses in plants derived from pathogentested (PT®) seed lines and non-PT seed lines was 2.2 and7.6% (1991),4.1 and 11.2% (1992), and 2.5 and 6.5% (1993) respectively. The levels of potato leaf-roll virus and severe mosaics were particularly low in crops grown from PT® seed. Virus incidence was generally low apart from individual crops with high potato virus X, potato virus S (PVS), or potato virus Y (PVY) levels (these crops were often from saved seed tubers). The incidence of PVY N appears to have been contained through the use of PT® seed, but the identification of PVS A and the rediscovery of potato virus A and potato virus M are of some concern. Suggestions for improvements to seed quality control are discussed.H95034
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