Pollination effects on patterns of ovule fate in Hesperis matronalis (Brassicaceae)

We examined ovule positional effects on patterns of ovule development within linear fruits of the invasive weed, dame’s rocket, Hesperis matronalis L. Fruits were collected from two sites in southwestern Ontario, Canada. The majority of ovules within fruits were aborted early in development. Emergent patterns of ovule abortion and seed maturation within fruits were nonrandom and dependent on ovule position. The probability of seed maturation within individual fruits decreased significantly from basal to distal ends, suggesting an intrafruit resource gradient. Self-pollinated flowers at one site produced fruits with a similar pattern of seed maturation as was found for open-pollinated plants. However, cross-pollinated flowers produced fruits in which the pattern of seed maturation was reversed; more seeds were matured at the distal ends rather than the basal ends of fruits, indicative of a fertilization gradient. Analysis of pollen-tube growth showed that ovule failure may not be attributed to pollen limitation. For seeds produced via hand-pollinations, we found no relationship between seed mass and seedling biomass, although seeds from self-pollinations germinated more readily than did seeds from cross-pollinations. While patterns of ovule fate in H. matronalis can be manipulated by pollen source, the effects of such patterns on plant fitness are yet to be determined.

Effect of ovule position on patterns of seed maturation and abortion in Robinia pseudoacacia (Fabaceae)

I examined the effect of ovule position on patterns of ovule development within the linear pods of black locust, Robinia pseudoacacia L. Fruits were sampled from three sites in southwestern Ontario, Canada. Approximately two-thirds of all ovules failed to show visible signs of fertilization or development. Patterns of seed maturation and abortion within fruits were nonrandom and depended on ovule position. The probability of seed maturation within individual fruits decreased significantly from the distal to basal ends, suggesting the existence of a fertilization gradient. Seeds at the basal ends of fruits were also lighter than more distally located seeds. While seed mass did not influence the likelihood of germination, seed mass was positively correlated with seedling size. Hence, ovule position exerts an influence on offspring vigour and has the potential, ultimately, to affect plant fitness.

Cucumber (Cucumis sativusL.) seed performance as influenced by ovary and ovule position

The performance of cucumber (Cucumis sativusL.) seeds in relation to ovary and ovule position was monitored during seed production. Seeds from three (first, seventh and tenth nodes) fruit positions and three (stylar, intermediate and peduncular) ovule positions were harvested serially during development and characterized with physiological and cellular markers. Seed moisture contents declined to 30%approx. 35 d after pollination (DAP) and remained constant thereafter. At 42 DAP the maximum dry weight was acquired in seeds except those from peduncular segments, whose dry weight accumulation lagged behind. The onset of germinability and desiccation tolerance occurred before the attainment of maximum dry weight, whereas seed performance, as shown by laboratory germination and greenhouse emergence, was largely improved after the completion of seed development. Cell cycle activities (DNA per nucleus and β-tubulin content) ceased by 28 DAP, whereas the degradation of seed chlorophyll continued during the entire maturation period. Seeds from the top fruit and from the peduncular fruit segments were delayed in reaching maximum quality compared with seeds from other positions, and this was correlated with a slower decline of chlorophyll fluorescence.

Effect of ovule position on seed maturation and seed weight in Ulex europaeus and Ulex gallii (Fabaceae)

We examined the effect of ovule position within the pod on the probability of seed maturation and on seed weight in two woody legumes, Ulex europaeus and Ulex gallii. Results showed that ovule position had a significant effect on the probability of seed maturation in both species. Ovules in a central position were found to have a higher probability of maturation in U. europaeus, whereas those in a stylar position were favored in U. gallii. Ulex europaeus showed no effect of position on seed weight. The smallest seed within the pod was more frequently at stylar positions in U. gallii. These results might be explained by several non-exclusive hypotheses: time of fertilization, constraints on seed development (e.g., fruit shape and access to maternal resources), and genetic quality. The effects of seed weight on progeny performance estimated as probability of germination and seedling weight were tested in a laboratory experiment. Neither U. europaeus nor U. gallii exhibited any effect of seed weight on the probability of germination. However, seedling weight was dependent on seed weight in both species. Keywords: woody legumes, probability of maturation, seed position, seed weight.

THE EFFECT OF OVULE POSITION ON THE FREQUENCY OF HYBRID AND INBRED SEED IN FABA BEAN

The effect of ovule and ovary position on the frequency of hybrid seed production of faba bean (Vicia faba L.) was measured at Dijon, France and Saskatoon, Canada. Even though there was far greater ovule fertilization frequency at Dijon (72%) than at Saskatoon (30%) the frequency of hybrid seed was significantly greater at Saskatoon (24%) than at Dijon (15%). Neither the position of the ovule within the ovary nor the position of the raceme on the stem had any effect on the production of hybrid seed. However, at both locations the highest position within a raceme produced a significantly greater proportion of hybrid seeds. It is proposed that under the effect of intra- or inter-plant stress, developing ovaries containing hybrid embryos may be selectively retained.Key words: Vicia faba, ovule fertilization, outcrossing, faba bean