Search Results

You are looking at 31 - 40 of 54 items for

  • Author or Editor: Michael J. Havey x
Clear All Modify Search

Genetic linkage maps have been proposed as tools for crop improvement. We constructed a genetic linkage map of cucumber including RFLP, RAPD, isozyme, and disease resistance markers. The map was used to determine the number, magnitude of effects, and action of genes conditioning quantitatively inherited fruit-quality traits, including length, diameter, seed cavity size, and color. Traits were evaluated in a replicated field trial over 2 years. A mating design was employed to confirm putative trait loci across generations and estimate overall genetic variances for the quality traits. For some traits, gene number estimates were similar to previously published reports employing biometrical methods.

Free access

Cucumber (Cucumis sativus) production is negatively affected by Zucchini yellow mosaic virus (ZYMV). Three sources of ZYMV resistance have been commercially deployed and all three resistances are conditioned by a single recessive gene. A vacuolar protein sorting–associated protein 4-like (VPS4-like) gene has been proposed as a candidate for ZYMV resistance from cucumber line A192-18. We analyzed the genomic region across the VPS4-like gene for three independent sources of ZYMV resistance in cucumber (A192-18, Dina-1, and TMG-1) and identified three haplotypes across the coding region and considerable variation in the introns. However, the haplotypes in the coding regions of the VPS4-like gene of A192-18, Dina-1, and TMG-1 encode the same protein sequence, revealing the genetic uniformity for ZYMV resistance from diverse germplasm sources.

Free access

Onion (Allium cepa L.) bulb color is controlled by at least five major loci (I, C, G, L, and R) and seedcoat color by one locus (B). The authors developed families segregating for bulb and seedcoat colors, simple sequence repeats (SSRs), and single nucleotide polymorphisms (SNPs) in genomic amplicons of dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS). The B and C loci were linked to SSRs on chromosomes 1 and 6 respectively. For all of three families, SNPs in DFR cosegregated with the R locus conditioning red bulb color. In the family from B2246 × B11159, red bulbs versus yellow bulbs were controlled by DFR and a locus (L2) linked at 6.3 cM to ANS. The authors propose that yellow bulb onions have been independently selected numerous times and that yellow populations carry independent mutations in structural or regulatory genes controlling the production of red bulb color in onion.

Free access

The amounts and types of epicuticular waxes on onion (Allium cepa) leaves affect feeding damage by onion thrips (Thrips tabaci). This study used gas chromatography mass spectrometry (GCMS) to establish the identities of waxes and measure over time wax amounts on leaves of inbred onion plants with glossy, semiglossy, and waxy foliage. Nine waxes were detected on leaves of all inbreds, and higher coefficients of variation (cv) were observed for less abundant waxes on foliage of doubled haploid onions. Older leaves had higher amounts of waxes compared with younger leaves on the same plant. Except for one minor wax, amounts of individual waxes on leaves were not significantly different for plants of different ages. There was a significant inbred by sampling date interaction due to lower amounts of waxes on the leaves of older plants from the semiglossy inbred. These results indicate that there is little advantage to multiple samplings of leaves over time from the same plant and resources may be better used to evaluate more plants. The relatively large cvs for amounts of specific waxes may reduce response to selection for unique epicuticular wax profiles to develop onion populations that suffer less feeding damage by onion thrips.

Open Access

The production of doubled haploid plants is desirable as an alternative to sexual inbreeding of longer-generation crops. Onion (Allium cepa L.) is a biennial plant and amenable to the production of gynogenic haploids. Although a strong population effect has been observed for gynogenic haploid production, there is no report describing the genetic basis of greater haploid production in onion. We evaluated over years the frequency of haploid production among onion inbreds and identified lines showing significantly (P < 0.01) greater production of haploids. The onion inbreds, B0223B and B2923B, produced the highest mean frequencies of haploids so far reported. Hybrid families from crosses of B2923B with inbreds having relatively low haploid production showed significantly higher haploid production than the low-producing parent and significantly lower haploid production than B2923B. Plants from B0223B and B2923B with established rates of haploid production were testcrossed and/or self-pollinated. The F1 family from B1717A-1 × B2923B-3 showed rates of haploid production slightly greater than the low parent (B1717A-1) and significantly less than the high parent (B2923B-3). Self-pollination of plants from B2923B showing relatively high rates of haploid production generated S1 progenies also producing relatively high frequencies of haploids. Selfed progenies from plant B2923B-6 showed a high mean rate of haploid production (56.8% ± 14.5%) and, more importantly, the highest level of haploid production (82.2%) reported for any single onion plant. These results indicate that relatively high haploid production, at least for B2923B, was quantitatively inherited with dominance towards low production. We suggest S1 family selection as an effective method to increase gynogenic haploid production of onion populations.

Free access

Cytoplasmic effects on plant performance have been documented, but are not well understood. Cucumber (Cucumis sativus) is a useful plant for studying organellar effects on phenotypes because chloroplasts show maternal transmission and mitochondria paternal transmission. We produced doubled haploids (DH) from divergent cucumber populations, generated reciprocal hybrids in a diallel crossing scheme, measured fresh and dry weights of plants 22–30 days after planting seed, estimated combining abilities and heterosis for early plant growth, and assessed performance differences between reciprocal hybrids with identical nuclear genotypes. Across experiments, general and specific combining abilities and reciprocal effects, as well as their interactions with replicated experiments, were all highly significant (P < 0.001). Hybrids consistently out-performed parental lines with average heterosis over midparent values between 14% and 30%. A mitochondrial mutant (MSC3) showed negative effects when used as the male due to paternal transmission of mitochondria, but not as the female parent. Reciprocal hybrids among wild-type DH parents were identified that differed significantly (P = 0.032 to 0.001) for dry and fresh weights across experiments, indicating that cucumber breeders should evaluate both directions of crosses when producing hybrid cultivars. Reciprocal hybrids from DH cucumbers offer a unique opportunity to study biological factors contributing to significantly better performances, due to specific nuclear-cytoplasmic combinations and/or parent-of-origin effects in identical nuclear backgrounds.

Free access

Fructans are the main soluble carbohydrate in onion (Allium cepa) bulbs and their concentrations show significant correlations with dry weights and pungency. In previous research, we identified regions on chromosomes 5 and 8 associated with higher amounts of soluble carbohydrates in onion bulbs. In this research, we estimated the genetic effects and interactions between these two chromosome regions using larger inbred families grown in field trials over 3 years. Bulbs were evaluated 30 and 90 days after harvest (DAH) for dry weights and soluble carbohydrates. Fructan concentrations decreased significantly between 30 and 90 DAH, consistent with loss of bulb dormancy over this period. Dry weights were negatively correlated with fructose and positively correlated with sucrose and fructans. Analyses of variance and interval mapping revealed that the region on chromosome 5 affected bulb dry weight, whereas the region on chromosome 8 significantly affected both dry weight and fructan concentrations. Regions on chromosomes 5 and 8 showed dominance for increased dry weights and/or soluble solids. Interactions between regions on chromosomes 5 and 8 were significant only for sucrose and the fructan neokestose, indicating that these regions independently contribute to higher amounts of soluble carbohydrates. These results demonstrate that onions with low concentrations of soluble carbohydrates were developed by selecting for relatively few recessively inherited chromosome regions.

Free access

The amounts and types of epicuticular waxes on onion (Allium cepa) leaves affect the severity of feeding damage by onion thrips (Thrips tabaci), a serious insect pest of onion. Onion plants with light green leaves are referred to as “glossy” and accumulate less epicuticular wax relative to the blue–green (“waxy”) foliage of wild-type onion. The onion cultivar Odourless Greenleaf (OGL) has visually glossy foliage, shows resistance to thrips feeding damage, and has the unique profile of accumulating waxes with 28 or fewer carbons. Plants of glossy OGL were crossed with the glossy inbred B9885 and waxy inbred lines DH2107, DH066619, and B8667. Hybrid progenies from glossy OGL by waxy plants had waxy foliage, indicating recessiveness of the glossy OGL phenotype relative to the waxy phenotype. Hybrids from the cross of glossy OGL with glossy B9885 were also waxy, revealing different genetic bases for the glossy phenotype in these two onions. Hybrid plants were self-pollinated and segregations in F2 families from OGL × waxy crosses fit the expected 3:1 ratio for the single locus at which the homozygous recessive genotype conditions glossy foliage. Segregations in F2 families from crosses of glossy 9885 × glossy OGL fit the 9:7 ratio, supporting two independently segregating loci, where the recessive genotype at either locus conditions the glossy phenotype. Amounts and types of epicuticular waxes on leaves of F2 progenies from crosses of OGL × waxy B8667 and glossy B9885 × OGL were determined using gas chromatography-mass spectrometry. Single-nucleotide polymorphisms were genotyped and genetic maps were constructed. The visually glossy phenotype from OGL and its unique profile of epicuticular waxes were conditioned by one locus on chromosome 6, for which we propose the name gl ogl . Onion populations such as OGL with unique epicuticular wax profiles will be important germplasms for the development of onion cultivars that suffer less feeding damage from onion thrips compared with waxy onion.

Open Access

Nuclear RFLPs were used to estimate relationships among 14 elite commercial inbreds of bulb onion (Allium cepa) from Holland, Japan, and the United States. Variability for known alleles at 75 RFLP loci and 194 polymorphic fragments revealed by 69 anonymous cDNA probes and a clone of alliinase were scored to yield genetically characterized and uncharacterized data sets, respectively. The inbred onion populations possessed more than two alleles at 20 of 43 (46%) codominant RFLP loci. Relationships among the inbreds were estimated by cluster analysis of simple-matching (genetically characterized data) and Jaccard (genetically uncharacterized data) coefficients using the unweighted pair group method and agreed with known pedigrees. RFLPs confidently distinguished among elite inbreds within and between specific market classes. RFLP profiles for virtual hybrids were computer-generated by combining gametic arrays among inbreds of the same market class and analyzed as described above. Allelic and genetically uncharacterized RFLPs confidently distinguished among these hybrids, even though heterozygosity for many markers produced a majority of monomorphic fragments. We randomly sampled decreasing numbers of RFLPs from the complete data sets and calculated simple-matching and Jaccard distances, noting the numbers of probes that were unable to distinguish any two inbreds or hybrids. As few as 10 polymorphic probe-enzyme combinations distinguished among all the inbreds and samples of 20 genetically characterized or 10 genetically uncharacterized clones distinguished all the virtual hybrids. This study demonstrated that the previously reported few RFLPs observed among open-pollinated (OP) onion populations were due to the highly heterozygous nature of the OP population.

Free access

Natural variation exists in onion (Allium cepa L.) for amounts of epicuticular waxes on foliage, and plants with lower amounts of these waxes suffer less feeding damage from onion thrips (Thrips tabaci Lind.). Wild-type onion possesses copious amounts of epicuticular waxes and is often referred to as “waxy.” The recessively inherited “glossy” phenotype has significantly less wax relative to waxy types and shows resistance to onion thrips but is vulnerable to spray damage, foliar pathogens, and excessive transpiration. Phenotypes visually intermediate between waxy and glossy also exist in onion, which we refer to as “semiglossy.” Epicuticular waxes on the leaves of glossy, semiglossy, and waxy onions were evaluated for appearance using scanning electron microscopy (SEM) and amounts and types were analyzed using gas chromatography/mass spectrometry. Wax crystals were clearly visible on the surface of waxy foliage with decreasing amounts on semiglossy and none on glossy leaves. The ketone hentriacontanone-16 was the most prevalent wax on leaves of waxy onion and was significantly (P < 0.01) less on semiglossy relative to waxy plants and on glossy relative to waxy and semiglossy plants. Numbers of adult and immature onion thrips were significantly reduced (P < 0.05) on glossy and/or semiglossy accessions relative to waxy in field and greenhouse cage experiments. These results indicate that semiglossy plants possess intermediate amounts of epicuticular waxes that may protect leaves from diseases or environmental stresses while still conferring resistance to onion thrips. Therefore, the semiglossy phenotype should be useful in integrated programs managing this important onion pest.

Free access