The first single-nucleotide polymorphism (SNP) maps for watermelon [Citrullus lanatus (Thunb.) Matsum. et Nakai] were constructed and compared. Three populations were developed from crosses between two elite cultivars, Klondike Black Seeded × New Hampshire Midget (KBS × NHM), an elite cultivar and wild egusi accession, Strain II × PI 560023 (SII × Egusi) and an elite cultivar and a wild citron accession, ZWRM50 × PI 244019 (ZWRM × Citroides). The SII × Egusi and ZWRM × Citroides F(2) populations consisted of 187 and 182 individuals respectively while the KBS × NHM recombinant inbred line (RIL) population consisted of 164 lines. The length of the genetic maps were 1,438, 1,514 and 1,144 cM with average marker distances of 3.8, 4.2, and 3.4 cM for the KBS × NHM, SII × Egusi and ZWRM × Citroides populations, respectively. Shared markers were used to align the three maps so that the linkage groups (LGs) represented the 11 chromosomes of the species. Marker segregation distortion were observed in all three populations, but was highest (12.7 %) in the ZWRM × Citroides population, where Citroides alleles were favored. The three maps were used to construct a consensus map containing 378 SNP markers with an average distance of 5.1 cM between markers. Phenotypic data was collected for fruit weight (FWT), fruit length (FL), fruit width (FWD), fruit shape index (FSI), rind thickness (RTH) and Brix (BRX) and analyzed for quantitative trait loci (QTL) associated with these traits. A total of 40 QTL were identified in the three populations, including major QTL for fruit size and shape that were stable across genetic backgrounds and environments. The present study reports the first SNP maps for Citrullus and the first map constructed using two elite parents. We also report the first stable QTL associated with fruit size and shape in Citrullus lanatus. These maps, QTL and SNPs should be useful for the watermelon community and represent a significant step towards the potential use of molecular tools in watermelon breeding.

Reliable yield performance is important in cucumber because seed companies prefer to market cultivars adapted to multiple rather than single regions of the U.S. Also, growers benefit by using a cultivar that performs well in many environments. Future performance of cultivars is also important. The objectives of the study were to (i) evaluate the yield of cucumber genotypes over successive years and in different locations, and (ii) identify cucumber genotypes with high stability for yield. A diverse set of 22 pickling genotypes was evaluated over 3 years (1986, 1987 and 1988) and in 7 locations across the United States. Yield traits were evaluated using once-over harvest and counting the number of fruit that were marketable, culled or oversize. Total yield, marketable yield (total minus culled fruit), early yield (number of oversize fruit), percent culls and fruit per plant were calculated. Data were analyzed with SASGxE and RGxE programs using SAS and R programming languages, respectively. There were strong effects of environment(E) as well as genotype(G) xE interaction for all traits. Genotypes ‘Regal F1’, ‘Calypso F1’, ‘Carolina F1’, ‘Gy 3’, ‘Gy 14’ and ‘Fremont F1’ had high marketable yield and medium to high stability for all traits. There was an advantage of hybrids over inbreds for trait performance. Hybrids fell into a single cluster with large prediction intervals. Based on the stability statistics and divisive clusters, it appears possible to breed stable cucumber genotypes with high yield. The genotype with highest performance for marketable yield, greatest stability for yield, lowest 1-R2 ratio value (diverse and representative) were ‘Marbel F1’ and Gy 14.

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Aminoethoxyvinylglycine (AVG) at 50,100, and 200 ppm induced staminate flowers on 3 gynoecious cucumber lines in the greenhouse. Both the time of application and the type of water used to prepare the AVG solutions had a significant effect on the node at which conversion from pistillate to staminate first occurred and on the total number of nodes bearing staminate flowers. Plants treated with 100 and 200 ppm AVG were chlorotic for about 10 days after application.

Silver nitrate and gibberellin A4/A7 (GA4/7) were compared for induction of staminate flower production on an inbred gynoecious cucumber (Cucumis sativus L.) line grown in the field at Madison, Wisconsin. Foliar sprays of silver nitrate at 100, 200, and 400 ppm induced significantly more staminate flowers per plant than did GA4/7 at the standard, widely-used rate of 50 ppm, making gynoecious x gynoecious hybrid seed production commercially feasible. The strong induction all plants treated with silver nitrate should minimize the genetic shift toward maleness observed from one generation to the next when GA is used to increase seed of gynoecious parental lines.