In P. affinis, pin pollen is shorter on average than thrum pollen. Pins have more coronal hooks on stigmatic papillae than thrums, but gaps between papillae are relatively smaller for thrums. Pin stigmas receive more pollen than thrum stigmas. Thrum stigmas receive more (dissortive) pin pollen, but pin stigmas are assortively pollinated. Pollen only germinates when trapped below papilla coronas. On thrum stigmas, most trapped pollen is pin. Pollen germination is better on thrum stigmas than pin stigmas, and thrum stigmas show a close relationship between numbers of legitimate pollen grains, numbers of germinating grains, and numbers of pollen tubes in the style. There is no inhibition of illegitimate pollen germination. Illegitimate pollen tubes are inhibited in the style. Incompatibility operates by a combination of dissortive pollination, dissortive pollen trapping, and stylar pollen tube inhibition. All heteromorphic features differing between pins and thrums are implicated in the inhibition of within‐morph fertilization in thrums.

Abstract:In field and laboratory experiments, enhanced degradation of the dicarboximide fungicides, iprodione and vinclozolin, was stimulated by only one application of the fungicides in a soil with no previous history of any pesticide input. Field and laboratory studies demonstrated the ease of stimulation by pretreatment with even very low concentrations of the fungicides (0.5 pg g-' soil) and at a range of temperatures and soil moisture conditions. Soils that had acquired full enhanced degradation could rapidly degrade fungicide applied at 30 times the recommended field rate. Cross-enhancement of degradation was noted with both fungicides, but not with their common metabolite, 3,5-dichloroaniline. Application of the antibiotics chloramphenicol or rifampicin to soil reduced enhanced degradation to control levels; cycloheximide had no effect. This, together with the inhibitory action of aide, mercuric chloride and repetitive microwaving, indicated that the agent(s) of enhanced degradation was probably bacterial.

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Enhanced degradation of the fungicide vinclozolin was stimulated by multiple successive applications to a soil without any history of previous pesticide input. A vinclozolin-degrading bacterium isolated from this soil was identified as a strain of Pseudomonas putida. This organism metabolised vinclozolin as a source of carbon, but it would neither grow with nor transform any other closely related dicarboximide fungicides nor the degradation product, 3,5-DCA. The degradation of vinclozolin by cultures of P. putida St-1 was investigated under various culture conditions; biodegradation was optimal at 23"C, pH 6-5 and inoculum densities of lo7 cells ml-' but cultures would grow from as little as 100 cells ml-l. Amendments of the vinclozolin-degrading isolate to soil previously untreated with the fungicide caused rapid degradation of applied vinclozolin, whereas amendments of boiled cells, or viable cells grown in the absence of vinclozolin, produced no discernible effect on the rate of vinclozolin degradation.