The inability to achieve adequate pollination of seed parents has slowed the development of hybrid carrots (Daucus carota L.) and dampened industry acceptance. Thus, cytoplasmically male-sterile inbreds and F1 seed parents were compared with their fertile counterparts for synchrony of floral events and character of pollinator foraging stimuli. Usually, but not always, male-sterile plants were visually different, bloomed later, and exhibited delayed nectar and aroma production compared to male-fertiles. The quality and quantity of nectar and aroma were also different, with male-sterile flowers often inferior to fertile flowers in amounts of nectar produced. Successful use of any cross-pollinated entomophilous hybrid crop system should involve selection for similar floral characteristics early in the breeding program to insure maximum transfer by insects of pollen from male-fertile to male-sterile parents.
A study of foraging by honey bees (Apis mellifera L.) among cytoplasmically male-sterile and malefertile seed parents of carrot (Daucus carota L.) revealed that honey bee discrimination between the fidelity to carrot phenotype and genotype were evident and often extreme. Some lines were extensively visited while others were virtually ignored. Wide differences in seed set were evident among male-sterile F1’s and inbreds and malefertile lines. Differences in seed yield were correlated with foraging preferences, but the quality of nectar from the stomachs of bees was not.
Examination of flowers of carrot (Daucus carota L.) using the scanning electron microscope revealed that some cytoplasmically male-sterile genotypes exhibit flower abnormalities that may be associated with reduced pollination and seed set. Such abnormalities, evident in many inbred lines, may carry over to the male-sterile F1 parents used to produce 3-way hybrids and probably affect insect pollinator activity.
Nectary development in cytoplasmic male sterile (cms) Brassica campestris L. was partially restored through 3 cycles of selection for nectary size and number. No major anatomical differences between nectaries of normal and cms plants were apparent under light and scanning electron microscopes (SEM). Half-sib family analysis of nectary development showed negligible additive genetic variance but a prominent maternal effect. Differential response to selection observed in 3 pedigrees suggests the possibility of capitalizing on nuclear-cytoplasmic diversity for the improvement of nectary function.
In addition to managing soilborne diseases, grafting with vigorous rootstocks has been shown to improve yield in tomato (Solanum lycopersicum L.) production. However, the influence of different levels of nitrogen (N) and irrigation supplies on grafted tomato plants has not been fully examined in comparison with non-grafted plants, especially under field conditions. The objective of this two-year study was to determine the effects of different irrigation regimes and N rates on yield, irrigation water use efficiency (iWUE), and N use efficiency (NUE) of grafted tomato plants grown with drip irrigation in sandy soils of north Florida. The determinate tomato cultivar Florida 47 was grafted onto two interspecific hybrid rootstocks, ‘Beaufort’ and ‘Multifort’ (S. lycopersicum × S. habrochaites S. Knapp & D.M. Spooner). Non-grafted ‘Florida 47’ was used as a control. Plants were grown in a fumigated field under 12 combinations of two drip irrigation regimes (50% and 100% of commonly used irrigation regime) and six N rates (56, 112, 168, 224, 280, and 336 kg·ha−1). The field experiments were arranged in a split-plot design with four replications. The whole plots consisted of the irrigation regime and N rate combination treatments, whereas the subplots represented the two grafting treatments and the non-grafted plants. Self-grafted ‘Florida 47’ was also included in the 100% irrigation and 224 kg N/ha fertilization treatment as a control. In 2010, the 50% irrigation regime resulted in higher total and marketable yields than the 100% irrigation regime. Tomato yield was significantly influenced by N rates, but similar yields were achieved at 168 kg·ha−1 and above. Plants grafted onto ‘Beaufort’ and ‘Multifort’ showed an average increase of 27% and 30% in total and marketable fruit yields, respectively, relative to non-grafted plants. In 2011, fruit yields were affected by a significant irrigation by N rate interaction. Grafting significantly increased tomato yields, whereas grafted plants showed greater potential for yield improvement with increasing N rates compared with non-grafted plants. Self-grafting did not affect tomato yields. More fruit per plant and higher average fruit weight as a result of grafting were observed in both years. Grafting with the two rootstocks significantly improved the irrigation water and N use efficiency in tomato production. Results from this study suggested the need for developing irrigation and N fertilization recommendations for grafted tomato production in sandy soils.