The effect of 5 temperature regimes and 10 urediniuf.J1 densities on urediniospore produc tion, latent period, and infectious period of a New Zealand isolate of Puccinia hordei Dtth on 'Zephyr' barley was investigated. Increasing ambient temperature in the range 10°-25°c decreased the length of the latent period and increased total urediniospore production during lhe infectious period. In all cases the spore production curve was negatively skewed. The length of the infectious period was not significantly affected by temperatures between 10°-20°c, but it was less at 25°c. Increasing uredinium density from 1/cm 2 to 161/cm 2 leaf area decreased uredinium size, urediniospore production per uredinium, and lengths of infectious and latent periods, but spore production per unit area of uredinium and the rate of uredinium eruption were both increased. Terminology of the rust infection cycle is discussed in relation to bases for quantification and comparison between laboratories. 287
To determine their importance as virus vectors, 1419 alate aphids were collected, mainly from field plots of garden peas (Pisum sativum L. var. sativum L.) in spring 1966, 1967, and 1968; 55% were Aulacorthum solani (Kltb.), 25% Myzus persicae (Sulz.), 16% .'I1acrosiphum euphorbiae (Thos.), and 3% Aphis craccivora Koch. Alatae of each species were transferred either singly or in groups to subterranean clover (Trifolium subterraneum CY. Bacchus Marsh) test plants. The viruses detected and their vectors were: (a) Subterranean clover red leaf virus (SCRLV), which caused the leaves of the test plant to be small and turn red as they matured. Alatae of A. solani often infected plants with SCRLV, and alatae of M. euphorbiae did so occasionally. In glasshouse tests SCRLV was l~ansmitted circulatively by apterae of A. solani but not by apterae of M. persicae or A. naccivora, although M. persicae appeared to transmit SCRL V when PELRV was also present. (b) Pea leaf roll virus (PELRV), which caused marked stunting of plants. Only some alatae of M. persicae infected the test plants. PELRV was transmitted circulatively by M. persicae but not by A. craccivora. (c) Bean yellow mosaic virus (BYMV), which caused mosaic symptoms in test plants; only a few alatae of M. euphorbiae were viruliferous. Glasshouse tests on field samples of pea plants with top-yellowing symptoms showed that these plants were infected more often with SCRLV than with PELRV. SCRLV was isolated also from field samples of lucerne, soyabean, and broad bean plants.
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