No abstract

The fungus Rhizoctonia solani Kühn and the root-lesion nematode Pratylenchus minyus Sher & Allen were closely and consistently associated in naturally occurring infections of winter wheat. The resultant root rot was characterized by markedly yellowed and stunted patches of plants in the wheat fields during spring growth. In greenhouse and field experiments the combined effects of the fungus and the nematode upon growth of the wheat was almost twice as great as the effect produced when either pathogen was controlled by a selective soil treatment. By pure culture techniques it was not possible to show that in the penetration of wheat roots the fungus was dependent upon the nematode or that the converse was true.

Pisum sativum vars. Early June, Early Sweet, and Sweet were grown in five root-rot soils and a sterilized control soil maintained at 28°, 26°, 24°, 22°, 18°, 16°, 14°, and 10 °C. Light intensity, day length, and soil moisture were kept constant. Data were recorded from seeding to mature plant development on loss of seed weight, gain in plant weight and height, losses due to preemergence killing and postemergence wilting, lesioning on the subterranean part of the epicotyls, and the fungi and nematodes found associated with the diseased tissues. Results showed that soil temperature generally, with distinct exceptions, had a definite influence on the growth of the peas, according to varieties, in the root rot soils. One fungus predominated as the causal agent of root rot for each variety: Fusarium spp. for var. Early June, which was highly tolerant to root rot soil, and Rhizoctonia solani for Early Sweet and Sweet, which were later maturing varieties. Pythium spp. was also involved in the root rot. The number of seedlings lost as a result of preemergence killing showed greater variation in relation to pea variety and root-rot soil than soil temperature, but postemergence wilting was correlated more closely with soil temperature. The variety Early Sweet was so susceptible to root rot over a wide range of soil temperatures as to preclude its general use in pea-growing areas.

The influence of photoperiod on sporulation of and infection by Helminthosporium turcicum Pass. (Trichometasphaeria turcica Luttrell), the causal agent of northern leaf blight of corn (Zea mays L.), was studied in growth chambers simulating normal, field weather conditions. The results were compared to an epidemic of the disease on sweet corn in Kent County, Ontario, in 1972 during a period of unusual weather conditions. An 8-h photoperiod was required to maintain both the diseased plants in a state of survival and the fungus in a state of repeated sporulating cycles on the plants in the growth chambers. The specific climatic component which could be correlated with growth chamber data was the photoperiod. Extremely wide temperature and rainfall variations from their long term means, and a low average exposure to light, contributed to the progress of the disease.

Chromatographic methods were used in an attempt to discover rvhy soybeans, which are highly susceptible to infection by D. phaseoloruw var. caulitora earlier in their development, become less susceptible as they grorv older.. Eighteen amino compounds in hydrolyzates of bark of soybean stems were identihed by co-chrornatography rvith substances of known ionstitution.An increase in concentration of cach colnpound u.as noted as stem tissue matured and became more rcsistant to infectior-r. Total nitrosen of the tissues studied also increased with plant maturitv.