introgression of the PR resistance on chromosome 4 into diverse onion populations. Table 3. Sequences of single nucleotide polymorphisms (SNP) on chromosome 4 of onion mapping within the 1.5 logarithm of odds (LOD) confidence interval for pink root-resistance in
levels of partial resistance to pythium root rot when compared with conventional cultivars. However, ‘Princettia Dark Pink’ had higher DSS in 2014 ( Table 1 ) and 2015 ( Table 2 ) than other hybrid cultivars. This cultivar exhibits a compact, mounding
structure of D. rosae and then to use the characterized races to identify genes conferring host resistance ( Debener et al., 1998 ; Whitaker et al., 2007a , 2007b , 2010a ; Yokoya et al., 2000 ). Isolates are distinguished from one another based on
Abstract
‘NuMex Sunlite’ is a bolting-resistant, pink root, [Pyrenochaeta terrestris, (Hansen) Gorenz, Walker and Larson] resistant, yellow grano-type onion (Allium cepa L.) developed for early fall planting. The release of ‘NuMex BR1’ as a bolting-resistant, yellow grano-type in 1981 had a significant impact on the New Mexico onion industry. Bolting resistance permits early planting and increases yield potential, and the greater plant development in cool season, resulting from early planting, helps control pink root losses, which are most severe in warm weather. More than one-half the New Mexico short-day crop in 1986 was ‘NuMex BR1’ ‘NuMex Sunlite’ resembles ‘NuMex BR1’ in bolting resistance, plant characteristics, and yield potential. ‘NuMex Sunlite’ has a higher level of pink root resistance than ‘NuMex BR1’ (Table 1), and is suggested for early fall planting on fields severely infested with P. terrestris.
Abstract
‘Ohio CR-6’ is a pink-fruited, tomato (Lycopersicon esculentum Mill.) hybrid adapted to greenhouse culture with resistance to Fusarium crown and root rot (Fusarium oxys-porum f. sp. lycopersici radieus). It was released by the Ohio Agricultural Research and Development Center in Aug. 1982.
The edible Alliums are economically important world-wide. The bulb onion (Allium cepa) is the most widely grown. The Japanese bunching onion (A. fistulosum) has many desirable characters, e.g., resistance to pink root, Thrips, smut, maggot, and Botrytis. Transfer of pink root resistance from A. fistulosum into A. cepa has been attempted for over 60 years. However, sterility of the F1 hybrid is a barrier and there is little evidence of gene introgression during backcrossing to A. cepa. Dr. Corgan has made crosses between A. fistulosum as the seed parent and A. cepa. He backcrossed the F1 hybrids to A. cepa and generated BC2 progenies which showed excellent pink root resistance. RFLPs in the chloroplast genome showed all BC2 progenies had either the normal or sterile cytoplasm of A. cepa. This may be due to not strictly maternal inheritance of the chloroplast DNA or a seed mixture during backcrossing. Other interspecific hybrids and their BC1 progenies had the cytoplasm of A. fistulosum. Nuclear RFLPs show hybrid patterns in the F1 plants. BC1 progenies possess some A. fistulosum markers as evidence of DNA introgression from A. fistulosum into the backcross progenies.
Abstract
Allium cepa L., A. fistulosum L., A. galanthum L., and A. cepa × A. fistulosum reciprocal interspecific hybrids were grown in vitro as calluses, shoots, and plantlets, and exposed to the filtrate of the pink root disease-causing fungus, Pyrenochaeta terrestris (Hansen) Gorenz, Walker, and Larson. Tissue culture reponses to the filtrate were assessed by visible damage ratings and fresh weights. Calluses exposed to the filtrate incorporated into the culture medium reflected the degree of whole plant susceptibility among the tester lines. However, in vitro shoot and plantlet culture responses did not reflect this correlation. Filtrate action appeared to be localized in meristematic cells. This in vitro approach may prove useful in screening or selection for onion pink root disease resistance.
-knot nematode (RKN) in field plots in 2010 at Mills River, NC, ‘Mountain Rouge’ and NC 161L were both highly resistant to RKN compared with ‘Pink Brandywine’, which had severe root galls. The Mi gene conferring RKN resistance in NC 161L originated from a
Callus cultures were established from intraspecific lines of Allium cepa L., interspecific F1 progeny of A. cepa crossed to A. fistulosum L. and to A. galanthum L., advanced generations of A. fistulosum x A. cepa backcrossed to A. cepa, and lines of A. fistulosum and A. galanthum. These genotypes had been identified as susceptible, resistant, or partially resistant tester lines based on prior seedling and field nursery screenings using the pink-root pathogen Pyrenochaeta terrestris (Hansen) Gorenz, Walker and Larson. Tester line calli were challenged in vitro with culture filtrates of the fungal pathogen and were assessed by visible damage ratings expressed as the percentage of pigmentation in response to the filtrate. The degrees of callus sensitivity to the filtrate observed in vitro corresponded well with the in vivo tester line classifications. These results eliminated the possible confounding influence of using various species of Allium for in vitro screening. Our results indicated the suitability of the in vitro screening approach for the possible identification of useful segregants or somaclonal variants possessing pink-root resistance. However, in vivo pathogenicity may involve mechanisms in addition to sensitivity to the putative toxins present in the filtrate.
Eighteen hybrid onion and 23 open-pollinated (OP) varieties were tested in southern New Mexico for plant characteristics, disease resistance, and bulb yield in order to determine if hybrid varieties outperformed OP varieties. Varieties were short- to intermediate-day in their bulbing response and were planted in the fall seasons of 1997 and 1998 and harvested the following May or June. Varieties were grouped based upon their relative maturity for fall-planted onions grown in southern New Mexico (early, intermediate, late). They were planted two (1998) or four (1997) rows per plot with plots being 8 ft (2.5 m) long and 22 inches (56 cm) wide. Plant stand per plot, plant height of seven plants, and leaf number of seven plants were measured 164 d after planting. Plots were harvested when 80% of the plant tops had fallen across all four replications of a single population. At harvest, number of seedstalks, number of bulbs, pink root incidence, and total bulb weight per plot were recorded. After removing culls, the percentage of marketable bulbs, marketable bulb yield, and average bulb size were determined. Hybrid varieties outperformed OP varieties for plant height, and leaf number but not for percentage of seedstalks, pink root incidence, percentage marketable yield, bulb size, and marketable bulb yield. In this study, most OP varieties perform as well or better than most of the hybrid varieties.