Some effects of rust infection and moisture stress on growth, diffusive resistance and distribution pattern of labelled assimilates in sunflower

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Abstract
Greenhouse experiments, where sunflower plants (cv. Peredovic) were inoculated with Puccinia helianthi at the vegetative stage of plant growth, showed that the effect of rust on growth parameters varied according to the moisture stress to which plants were subjected. Rust infection caused a marked reduction in the diffusive resistance of leaves in darkness. However, the diffusive resistance in light of leaves not stressed or subjected to mild moisture stress was unaffected by rust infection. In uninfected plants subjected to moderate moisture stress, the diffusive resistance in light increased markedly, whereas in rust-infected leaves it remained the same as in leaves not stressed or subjected to mild moisture stress. Carbon-14 uptake by the first pair of true leaves of non-stressed plants or those subjected to mild moisture stress was unaffected by a low level of rust infection (9% disease rating). Carbon-14 uptake by uninfected leaves was reduced when they were subjected to moderate moisture stress. Rust infection and moderate moisture stress caused a reduction in the rate of translocation of labelled assimilate from leaves fed with 14CO2 and also altered the distribution pattern of labelled translocate to various sinks.