Genetic improvement of carrot, onion, and garlic has depended upon introgression of alleles from foreign cultivars, from wild forms of cultivated species, and from wild species. Introgression of Asian germplasm in European carrots has resulted in more than a doubling of carotene content; wild carrot has provided two of the most widely used male-sterile cytoplasms for production of hybrids; and Daucus capillifolius has been used as a source of resistance to carrot fly. Onion male-sterile cytoplasm used for hybrid production has its origins in a species related to onion, while resistance to several diseases originated in foreign cultivars. Production of true garlic seed has depended on a broad germplasm base for its success. More examples and germplasm utilization strategies will be discussed.
Four carrot populations with low total sugar/low reducing sugar concentration, low total sugar/high reducing sugar concentration, high total sugar/low reducing sugar concentration, and high total sugar/high reducing sugar concentration were compared for pH 4.5 invertase, pH 7.5 invertase, sucrose synthase, and sucrose phosphate synthase activity. Invertase activities correlated well with reducing sugar concentration. Sucrose synthase and sucrose phosphate synthase activities were low in all populations. Total sugar level was not well-correlated with the activity of any enzyme measured. Developmental analysis indicated some reduction in enzyme activity as roots grew.
Central Asia is the center of origin for many Allium species and a rich genetic source of wild relatives of onion and garlic. For this reason germplasm collections of cultivated Alliums have targeted the acquisition of seed and bulb samples from this region, and several plant expeditions from Asia, Europe, and North America have collected Allium germplasm in Central Asia. Central Asian Allium germplasm has been valuable both as raw materials for scientific research leading to published data, and as starting materials for genetic improvement of the crop. Utilizing this germplasm it has been possible to improve garlic so it can be bred like other seed-propagated crops. Several interspecific crosses have been made between onion and other Central Asian wild relatives and these crosses have yielded useful traits for onion improvement. Allium germplasm from this region has also been important in elucidating the systematics and origins of diversity in onion and garlic. By any of these measures, Central Asian Allium collections have been valuable. Challenges and successes in collecting, maintaining, evaluating, and using these collections remain.
Diet is implicated globally in the cause and severity of many diseases, including cancer, heart disease, and diabetes, and a large body of medical evidence indicates that consumption of healthier foods can alleviate both the incidence and severity of not only these diseases, but also obesity, which is a causal factor for many chronic diseases. The 2010 Dietary Guidelines for Americans indicated that several nutrients are underconsumed in the United States, including folate, magnesium, potassium, dietary fiber, and vitamins A, C, and K. Vegetables and fruits are major sources of several of these micronutrients and minerals as well as many other phytonutrients. Despite these health benefits, vegetable and fruit intake by U.S. consumers is significantly lower than recommended by dietary guidelines (less than 40% of recommended intake) and has not risen in the past decade. Collaborations between horticultural plant breeders, production and postharvest scientists with food scientists, nutritionists, medical scientists, marketing specialists, and social scientists are needed to develop plans and take action to stimulate increased vegetable and fruit intake. Increased intake may have a positive impact not only on the health of consumers, but would also increase the economic value of horticultural commodities and raise the profile of horticultural sciences. Horticultural approaches to address this important challenge, and opportunity, must be developed.
Three orange-mesocarp derivatives of the xishuangbannan cucumber (Cucumis sativus L. var. xishuangbannanesis Qi et Yuan), P100, P101, and P104; and NPI (P105), an unrelated cucumber (Cucumis sativus L.) reported to have orange flesh, were selected as parents for a diallel experiment to evaluate inheritance of orange cucumber mesocarp pigment over 3 years. Visual color intensity and carotenoid content were closely related. A preponderance of additive genetic effects for cucumber mesocarp pigmentation was observed in grade size 2 fruit (immature fruit used for pickling). Both additive and nonadditive genetic effects were important in grade size 4 fruit (mature). Years and yea× genotype interactions were highly significant for pigmentation of size 2 fruit, indicating the importance of environment on the expression of pigmentation in this size class. In contrast, color development was stable among years for size 4 fruit. P104 exhibited high general combining ability (GCA) estimates for size 4 fruit pigmentation across years, while P101 had high GCA estimates for size 2 fruit. The diallel analysis illustrated high fruit carotene content of parents per se. However, most hybrid combinations of the diallel reduced carotenoid content relative to parents, indicating both dominance for low carotenoid content for both fruit sizes and lack of genetic complementation among parents to enhance fruit color. Genetic control of pigmentation in size 2 fruit appeared to be independent of that for size 4 fruit.
Diverse carrot (Daucus carota L.) inbreds were evaluated as young plants in the greenhouse and mature plants in the field for resistance to the pathogen Alternaria dauci (Kühn) Groves and Skolko. Persistence of leaves after infection was the criterion used to estimate disease damage by the pathogen. Partial resistance was identified. A five-parent diallel evaluated for resistance indicated a preponderance of additive variation with some dominant gene action for resistance. Reciprocal cross differences were significant for certain crosses. Responses of most inbreds were useful in predicting resistance in their hybrids, but exceptions to this trend did occur. Field resistance ratings generally correlated well with resistance ratings obtained in greenhouse, even in grower fields where fungicides were applied.
Carrot tissue cultures, germinating seed, and dry seed were exposed to gamma radiation. Irradiation accelerated germination of carrot seed in the M1 generation at low doses (0.5 and 1 krad), whereas higher doses delayed germination. A high negative correlation was observed between dose and survival of plants after seed irradiation. Plant size and root weight were 20 % to 35% greater than control plants after seeds, but not tissue cultures, were exposed to low doses of gamma irradiation. Higher doses reduced M1 plant size by >50% in germinating seed and tissue culture treatments but less for the dry seed treatment. Seed production decreased while phenotypic variation of M1 plants increased with increasing gamma ray dosage. Root weight and total dissolved solids were highly variable in M2 families. Less variation was observed in total carotene content and none was seen in sugar type (reducing vs. nonreducing sugars). Induced variation in root color and root shape was also observed. Irradiation of germinating seed and tissue cultures yielded more M2 variation than irradiation of dry seed. Putative point mutations were not observed. Unirradiated carrot tissue cultures did not yield significant M2 somaclonal variation. Average root weight of M2 plants increased with increasing gamma ray dosage, especially for the dry seed treatment.
Maize transposable elements, Activator (Ac) and Ds transformed into several heterologous plant species for transposon tagging of genes. Several genes in Arabidopsis, flax, petunia, tobacco, and tomato have been tagged and cloned by using Ac and Ds. We have double transformed carrot lines, B493 and B7262 with stabilized autonomous Ac and non-autonomous Ds element to develop a two-element based transposon tagging system. PCR and Southern hybridization indicated that Ds element transposed from T-DNA in calli, somatic embryos and transgenic plants. The insertion of Ds element into new sites in carrot genome after excision verified by GUS assay, Southern hybridization and inverse-PCR. Currently, the behavior of non-autonomous Ds element is being studied. Ds induced mutation will be screened in transgenic plants. These initial results demonstrate that the Ac/Ds-based transposon tagging system may work in carrot.