proposed to be a major cause of winter mortality. Because bolting, or the production of a flower stalk, results in a hard scape in the center of the bulb and reduces bulb size, it is undesirable during the production of bulbing onions. Bolting is triggered
Rebecca Grube Sideman, Amanda Brown, Ruth Hazzard, and Heather Bryant
John McCallum, Susan Thomson, Meeghan Pither-Joyce, Fernand Kenel, Andrew Clarke, and Michael J. Havey
Bulb onion is one of the most widely cultivated vegetables but is poorly characterized at the genetic level. It is a biennial, outcrossing diploid that exhibits severe inbreeding depression ( Havey, 1993 ) and is traditionally propagated from seed
Michael J. Havey
Although always among the top five vegetables in value, little genetic information has been published on the bulb onion. Genetic and molecular analyses are hampered by the plant's biennial nature, severe inbreeding depression, and huge genome. Research is underway to construct a low-density genetic map of onion based on RFLPs, AFLPs, and RAPDs. Among open-pollinated populations (OPPs), levels on DNA polymorphisms were in agreement with those of other outcrossing diploid species. However, we identified little putative-allelic diversity among the OPPs (1.9 polymorphic bands per polymorphic probe–enzyme combination) supporting a bottleneck during the domestication of onion. Our segregating family is from the cross of two diverse inbreds and will be used to map quantitative trait loci conditioning phenotypically correlated production (maturity, storability, and firmness), consumer-preference (pungency, flavor, and bulb shape), and health-enhancing (anti-platelet aggregation) attributes of onion. We are also attempting to tag chromosome regions controlling relatively simply inherited traits that are difficult or expensive to characterize classically.
Jongtae Lee, Sunkyoung Hwang, Seongtae Lee, Injong Ha, Haejun Hwang, Sangdae Lee, and Juyeon Kim
Onion ( Allium cepa L.) is one of the most important vegetable crops grown in Korea. Bulb onion growers reported a total area of 20,036 ha, producing 1.29 million tons of onions [ Statistics Korea (KOSTST), 2013] . The vast majority of this area is
Mau-Wei Lin, James F. Watson, and James R. Baggett
The inheritance of resistance to neck rot, incited by Botrytis allii Munn, was studied in four crosses between resistant and susceptible bulb onion (Allium cepa L.) lines, one cross between two resistant lines, and one cross between two susceptible lines. Using tests of excised scale pieces inoculated with a spore suspension and incubated in plastic boxes at 20C for 6 days, parents, F1, F2, and backcrosses were assigned disease indices (DI) derived from infection severity scores of individual bulbs. Generation means and frequency distribution of DI indicated that inheritance was quantitative and mostly additive with a small amount of dominance for susceptibility. Estimates of gene effects using a three-parameter model also indicated that additive effects predominated, with some dominance and no epistasis. Broad-sense heritability estimates ranged from 42% to 63% in the resistant x susceptible crosses.
Mau-Wei Lin, James F. Watson, and James R. Baggett
Analysis of parents and progeny generations of bulb onion (Allium cepa L.) crosses among parents with differing content of soluble solids (SS) and pyruvic acid (PA) showed that SS and PA are expressed and inherited in a quantitative manner. Distribution of SS and PA in both parents and progenies covered a range of values. Generation means, frequency distributions, deviation from midparent value, and estimates of gene effects all indicated that inheritance of SS and PA was additive, except for small deviations from the additive hypothesis in several individual backcrosses. Estimates of broad-sense heritability ranged from 48% to 53% for PA and 8 % to 56 % for SS. Phenotypic correlations between PA and SS estimated from the F2 generations of two crosses, were moderate and positive (r = 0.50 and 0.42).
Brad Geary, Deron Beck, and Mike Thornton
Botrytis neck rot, caused by Botrytis allii, is a major storage problem in dry bulb onions. This disease has been responsible for losses exceeding 50%, resulting in financial devastation to growers. Botrytis infections likely occur around the last month onions are in the field prior to harvest and before moving into storage. Earlier studies indicated that the spread of this fungus did not occur in storage. More recent studies suggest that bulb-to-bulb transmission in storage is possible, especially when bulbs are handled roughly during harvest. `Vaquero' dry bulb onions were planted in 2003 and 2004, and in 2005 the cultivar Renegade was used. All bulbs were produced using standard commercial practices. Bulbs were hand-lifted at harvest to reduce the amount of mechanical injury, then cured for 2 weeks. To simulate impact bruising, a 1/4-lb weight was dropped through a 2-ft PVC pipe, striking a healthy bulb on the outer scale. Shatter bruising occurred by dropping healthy bulbs down a 7-ft column containing seven offset immobile metal bars. To evaluate the interaction of inoculum load with bruise injury on disease spread, healthy bulbs were surface inoculated with botrytis and incubated until visible sporulation. Twelve infected bulbs were added to onion samples immediately after bruising. The treatments were then stored under ambient conditions. In 2004 and 2005, shatter bruising caused significant increases in botrytis infections to the inside and outside of the bulb over impact bruising, and impact bruising caused significantly more infections than the nonbruised check treatments. Adding botrytis infected bulbs increased infections, but only when injury of either type was present. Shatter bruising had the most significant effect on total botrytis infection.
James M. Bradeen and Michael J. Havey
Commercial bulb-onion (Allium cepa L.) growers often complain that hybrids they have grown successfully for a few years fail to perform at the expected level. Inbreds used to produce hybrid-onion seed rarely have been self-pollinated for more than two generations and retain a high level of heterozygosity. Over time, selection, drift, or contamination of inbreds may contribute to disappointing hybrid performance. We identified randomly amplified polymorphic DNA (RAPD) between two inbred onion lines, demonstrated their Mendelian inheritance, and tried to distinguish among and examine changes in independently maintained, publicly released inbred lines of onion. We observed poor agreement between data sets based on genetically characterized and uncharacterized RAPD markers. Our analyses used only genetically characterized RAPD markers and revealed that contamination, in addition to-drift and/or selection, likely contributed to differences among independently maintained, publicly released inbreds. However, RAPD markers were not able to distinguish confidently among four related inbreds. RAPD markers will be useful in Allium genetics and breeding, but identifying and characterizing reliable polymorphisms is critical.
manure were effective at improving soil OM content and soil fertility, especially in regards to long-term applications ( Haynes and Naidu, 1998 ; Prasad, 2009 ), the effectiveness of animal manure on bulb onion production was not always positive
Ockyung H. Bark, Michael J. Havey, and Joe N. Corgan
Allium fistulosum L. (bunching onion) is resistant to many of the important diseases and pests of Allium cepa L. (bulb onion). Although the first interspecific hybrids were generated more than 50 years ago, there is no conclusive evidence that any desirable trait in bunching onion has been successfully transferred to bulb onion by backcrossing. We identified RFLPs in the chloroplast and nuclear genomes to assess DNA transfer from bunching to bulb onion by backcrossing an interspecific hybrid to a bulb onion. Polymorphisms in the chloroplast genome established that the interspecific hybrid and three putative backcross plants had the cytoplasm of a bunching onion. All 57 random cDNA probes detected polymorphisms between the bulb and bunching onion for at least one of two restriction enzymes. The backcross progenies always possessed the bulb-onion fragments and an excess of probes detected the bunching-onion fragments. Only one plant showed an acceptable fit to the expected 1:1 backcross ratio. Significant deviations from expected segregation ratios may be the result of abnormal meiosis in the interspecific hybrid. However, these observations could also be explained by a previously proposed nuclear-cytoplasmic interaction conditioning preferential survival in the bunching-onion cytoplasm of eggs carrying bunching-onion chromosomes.