Bumblebees (Bombus spp.) are important pollinators of mostly self-sterile rabbiteye blueberry (Vaccinium ashei Reade). Annual bee colonies start from solitary overwintered queens who emerge in near-synchrony with rabbiteye blueberry bloom. Although colony populations may reach several hundred individuals by midsummer, in early spring most Bombus visiting rabbiteye blueberry are queens reared the previous season. Thus, practices that encourage production of queens in summer may increase populations of blueberry pollinators the next spring. In south Georgia, midsummer shortages of nectar-yielding plants may nutritionally limit queen production, and cultured bee forages may help overcome this deficiency. Candidate plants must not compete with the crop for pollinators, and they must be attractive to bees, easy to grow, vigorous, and non-invasive. In 3 years of trials, the following plants have shown promise as supplemental bumblebee forages in south Georgia: Althea (Hibiscus syriacus), abelia (Abelia ×grandifolia), vitex (Vitex agnuscastus), red clover (Trifolium pratense perenne), Mexican heather (Cuphea hyssopifolia), monkey grass (Liriope muscari), summer sweet (Clethra alnifolia), and giant sunflower (Helianthus giganteus).
G.W. Krewer, K.S. Delaplane, and P.A. Thomas
E. James Parrie and Gregory A. Lang
Pollen deposition on the stigmatic surface of blueberry pistils was studied with regard to maximum pollen load and stigmatic fluid production (stigma receptivity). Three hybrid southern highbush cultivars (Vaccinium corymbosum L. with V. darrowi Camp, V. ashei Reade, and/or V. angustfolium Aiton), two northern highbush cultivars (V. corymbosum), and one hybrid half-high cultivar (V. corymbosum with V. angustifolium) were selfand cross-pollinated with counted pollen tetrads until saturation of the stigmatic surface occurred. Stigmatic saturation generally required 200 to 300 tetrads and was characterized by the cessation of stigmatic fluid production and the inability to absorb further tetrads. The loss of stigmatic receptivity was irreversible. Cross-pollination resulted in cessation of stigmatic fluid production at lower levels of tetrad deposition than did self-pollination, suggesting a potential pollen-stigma recognition phenomenon. Northern highbush, half-high, and southern highbush cultivars required 7% to 10%, 12% to 17%, and 14% to 21%, respectively, more self-pollen to develop the stigmatic saturation condition. The potential relation of the pollenstigma phenomenon to self-incompatibility mechanisms is discussed.
Madhu Aneja, Thomas Gianfagna, Edward Ng, and Ignacio Badilla
The causes of poor fruit set of cocoa (Theobroma cacao L.) in the greenhouse were studied by examining factors that may influence pollen germination. Hand pollination of cocoa flowers resulted in 45.8% fruit set when flowers were pollinated within 3 hours of anthesis. Pollen germination did not occur until about 6 hours after pollination. Later pollinations (7 to 9 hours after anthesis) or earlier pollinations (16 to 18 hours before anthesis) did not lead to fruit set. Cocoa pollen did not germinate in vitro unless the excised flowers were incubated for 6 hours at 25C in closed vials. During the incubation period, CO2accumulated to a final concentration of about 85 ml·liter-1 as a result of respiration. Ethylene production was not detectable. Incubation of flowers with a NaOH-saturated wick, to absorb CO2, prevented pollen germination in vitro. Incubation of flowers at 15C also prevented pollen germination in vitro at 25C. Hand pollination of flowers 7 to 9 hours after anthesis or 16 to 18 hours before anthesis using CO2-incubated pollen resulted in about 10% fruit set. Enclosed pollinations in vivo, in which CO2 was allowed to accumulate, resulted in nearly 100% fruit set. The initial failure to set fruit from hand pollinations may result from poor or slow pollen germination. Moreover, CO,-incubated pollen might be used to increase fruit set in cocoa by extending the effective pollination period.
The seed-producing system of salvias (Salvia splendens Sello) was investigated. The number of florets opening per day per plant increased with the increase in days from anthesis. Pollinators that effectively worked were small-sized insects. High pollen viability was observed on the stigmatic surface, and pollen tubes reached the ovules within 3 hours after pollination. Fertilized ovules became mature seeds within 25 days after fertilization. Pollination within 1 day after opening of florets resulted in a high percentage of seed setting. The pollen-ovule ratios indicated that salvias were facultative xenogamous. Actually, the salvias had heterostyle florets and the ability to set seeds without pollinators.
J.R. Hotchkiss, P. Revilla, and W.F. Tracy
Cold tolerance useful for sweet corn improvement may be present in open-pollinated (OP) cultivars. Cold tolerance in sweet corn is the ability to germinate, emerge, and grow under low temperatures. The cold tolerance of 35 open-pollinated sweet corn populations and controls was measured by growing the entries under 14 °C day/10 °C night in growth chambers. The same entries were grown under warm (24 ± 2 °C) conditions in a greenhouse. Traits measured included percent and time to emergence, seedling color, and seedling root and shoot dry mass. Respective repeatability estimates calculated from mean squares were 0.08, 0.33, 0.33, 0.50, and 0.60 for these traits. Entries were ranked separately in each environment based on their performance using a rank-summation index. Differences in cold tolerance existed among the entries. Emergence ranged from 75% to 100% among the entries, with a mean of 90.9%. Time to emergence ranged from 16.2 to 21.9 d, with a mean of 18.2 d. Root and shoot mass ranged from 0.07 to 0.27 g/plot and 0.07 to 0.24 g/plot, respectively. Correlations among the traits measured were favorable, permitting simultaneous improvement. The rankings between the warm and cold environments were significantly correlated (r = 0.67***), indicating that some entries that performed well under low temperatures also performed well under warm conditions.
Pedro Revilla and W.F. Tracy
Heterotic patterns in sweet corn are weakly defined. Most sweet corn inbreds are descended from three open-pollinated cultivars: `Golden Bantam', Stowell's Evergreen', and `Country Gentleman'. Heterotic and phylogenetic relationships among these three cultivars and others are not clearly known. This investigation was designed to investigate the heterotic patterns among some historically important open-pollinated sweet corn cultivars: `Country Gentleman', `Golden Bantam', `Lindsey Meyer Blue', `Stowell's Evergreen', `Howling Mob', and `Pease Crosby'. The 15 possible hybrids from the diallel cross plus the 6 parents were grown in midspring and late summer plantings. Heterosis and combining ability effects were estimated for 13 traits. Hybrid × planting date interactions were significant for most of the main traits, hence, planting dates were analyzed separately. Average midparent heterosis for grain yield was 29.17% in the first planting date and 57.04% in the second planting. Midparent heterosis for yield and plant height were highest for hybrids with `Country Gentleman' as a parent. `Stowell's Evergreen' when crossed to `Pease Crosby', `Lindsey Meyer, and `Golden Bantam' exhibited high heterosis. The two late-maturity cultivars `Country Gentleman' and `Stowell's Evergreen' had higher general combining ability than the four early-maturity cultivars for most traits. Specific combining ability was seldom significant. Yield of `Country Gentleman' hybrids averaged over all crosses and planting dates was the highest. These data indicate a strong heterotic pattern—`Country Gentleman' × `Pease Crosby', `Golden Bantam', and `Lindsey Meyer Blue'—and a weaker one—`Stowell's Evergreen' × `Pease Crosby', `Golden Bantam', and `Lindsey Meyer Blue'.
Pedro Revilla and W.F. Tracy
Sweet corn is one of the most important vegetable crops in the United States, however the morphology and phylogeny of open-pollinated sweet corn cultivars has not been studied. Fifty eight open-pollinated sweet corn cultivars were characterized with thirty-four descriptors to provide information for breeders interested in broadening the genetic base of sweet corn. Principal component analysis and cluster analysis were performed to classify sweet corn cultivars based on morphology. Also, relationships among morphological variables in this set of cultivars were determined. The general ordination of cultivars followed an axis representing earliness, and plant, leaf, and tassel size, while ear and kernel attributes were less variable. The morphological variability among all of the widely used sweet corn cultivars, except `Country Gentleman', was not greater than the variability found among the `Golden Bantam' strains. Based on morphology, 52 of the cultivars could be considered as one race, which we propose be called `Northeastern Sweets'. These may be a subset of the race `Northern Flint'. Five of the remaining cultivars are from the north-central or southwestern United States and may represent races from those areas. The sixth cultivar is `Country Gentleman', a commercially important sweet corn cultivar. Due to the importance of `Country Gentleman' and the introgression of nonsweet germplasm into modern sweet corn, we believe that sweet corn should be defined based on its use as a vegetable and on the presence of one or more genes that increase sugar levels in the endosperm.
Michael J. Havey
selection of maintainer lines after crossing (i.e., at maximum linkage disequilibrium), they may not be in linkage disequilibrium with Ms among plants from open-pollinated (OP) populations ( Gökçe and Havey, 2002 ). Yang et al. (2012) identified two
Javier Sanzol and Timothy P. Robbins
work was to identify S-alleles in european pear by means of pollinations and subsequently analyze the correspondence between S-phenotypes and S-RNase genotypes. Following an approach based on the use of semicompatible cultivars, we were able to
Karen E. Mulford and James J. Linduska
Cucumbers are susceptible to the bacterial wilt organism that overwinters in the gut of cucumber beetles. This disease is transmitted in feces via open feeding wounds and plugs xylem vessels of water conductive tissues. Insecticides can be applied to control cucumber beetles. Adios, a semiochemical bait impregnated with cucurbitacin is combined with the insecticide carbaryl, which can be applied after plant emergence to control cucumber beetles. However, the method of application for giving the maximum control is unknown; thus, this was the purpose of this project. This study evaluates the rate of application, number of applications, methods of application using pressure and airblast sprays, and compares two Adios formulations. Also studied were the effects of Adios on bee fertilization and the quality of the fruit, since carbaryl is toxic to bees, and therefore can affect pollination. Adios was also compared to a foliar insecticide, Asana.