Common bacterial blight (CBB) in common bean (Phaseolus vulgaris L.), caused by Xanthomonas campestris pv. phaseoli (Xcp), reduces bean yields and quality throughout the world. Pinto `Chase' is a high-yielding variety with moderate resistance to Xcp derived from great northern Nebraska #1 selection 27, whose resistance is derived from an unknown tepary (P. acutifolius) bean source. XAN-159 is a black mottled small seeded breeding line with different genes for high resistance to Xcp derived from a different tepary source (PI 319443). Our objective was to pyramid different genes for Xcp resistance from the donor parent XAN-159 into the rust-resistant recurrent parent Pinto `Chase' using the classical back-cross breeding method with confirmation of resistance using RAPD molecular markers. Resistance was confirmed in some BC2F2 generation plants. Seven RAPD markers and the V locus (flower color) previously identified were confirmed in the BC1 and BC2 populations. Smaller seed size, purple flower color, and black mottled seed coat color were coinherited with resistance to Xcp. However, a recombinant plant with enhanced CBB resistance and moderate-sized pinto seed was identified. Backcross breeding is being continued.
Seeds of Lupinus havardii Wats. (Big Bend bluebonnet), a potential cut flower crop, were subjected to a variety of scarification and temperature treatments. Without scarification, only 10-20% of the seeds germinated within one week. Germination percentages increased sigmoidally as scarification time in concentrated sulfuric acid increased. Nearly 100% germination was obtained within one week after seeds were placed in sulfuric acid for 120 min. Nicking the seed coat with a razor blade also resulted in near 100% germination. Soaking the seed in water for 24 h failed to enhance germination. Soaking the seed in ethanol, methanol, or acetone for 2 h likewise failed to enhance germination. Total germination of scarified seed was >90% between 21 and 33C within 28 h. The most rapid germination occurred within a range of 24-29C. Above or below this range germination was delayed. At 35C, seedling, mortality was observed and total germination was reduced to <50%. Our data indicate that seed of this species requires scarification for optimum germination but the seed can germinate over a relatively wide temperature range.
Advanced, two-species CBC individuals were used to create the first-ever, three-species hybrids between P. acutifolius, P. coccineus and P. vulgaris. M6 (2 species) × H15 (3 species) is the only three-species hybrid to date that segregates for diagnostic traits. Three generations of M6 (F2, F3, F4,) were used to create the series. Hybrid breakdown was most severe with M6 F2 × H15, producing 100% cripples that died before anthesis. In M6 F3 × H15 hybrids, segregation for stigma position, flower color, germination type, growth habit, leaf length/width ratios, and seed morphology commenced in the F1 hybrid generation. F, phenotypes, with P. coccineus flowers & seeds and P. acutifolius leaves & growth habit, had severe hybrid breakdown with weak self compatibility; purple seed coats, with or without black circundatus markings, and new flower colors were also produced. F1's with P. vulgaris growth habits were self-fertile and ceased segregating after the F2.
Germination inhibitors found in parsley (Pertroselium hortense) seed have serious effects on field establishment. Studies have been conducted on chemical and physical attributes in relation to cultivar, age of seed and location of the seed on the seed stalk. Results indicate that the inhibitor is highly soluble in H2O and can be removed with as little as a half-hour aqueous wash. Soaking 30 g (∼500 seeds/g) of seed in an aerated graduated cylinder containing 100 ml distilled H2O for 24 hours then applied to radish, lettuce, and parsley seeds revealed complete germination inhibition of these seeds. Decreasing the soaking time did not reduce the inhibitory effects of the solution. Location of the inhibitor within the seed was found to be specific to the seed coat. The amount of inhibitor present varied with the cultivar and seed lot within that cultivar. Size and age of the seed had little effect on the amount and strength of the inhibitor. Location of the developing seed on the seed stalk effected the amount of inhibitor present. Primary umbels contained the least amount of inhibitor when compared to the secondary and tertiary umbels.
The germination of verbena (Verbena × hybrids) seed was found to be sensitive to high substrate moisture content. Cultivars varied in sensitivity to excessive substrate moisture content, with `Romance Scarlet' having higher total germination (G) in the presence of free water than `Showtime Blaze' or seedling `Red A'. Hilum cavity measurements of dry seeds showed larger hilum apertures with reduced depths for seeds of `Romance Scarlet' than for the others. Seed imbibition resulted in a rapid and extensive thickening of the hilum wall. The extent of hilum aperture closure varied among cultivars and the quantity of water present. Free water reduced hilum apertures 45% for `Romance Scarlet', 60% for `Showtime Blaze', and 86% for `Red A'. Seeds of `Romance Scarlet' and `Showtime Blaze' failed to germinate with lanolin covering the hilum, while seeds coated with lanolin, except for the hilum, had 67% to 78% G of nontreated seeds. This difference indicates that essential oxygen for the embryo was obtained through the hilum and micropyle of the seeds. Total germination varied with substrate moisture content, with seeds placed horizontally on 2%, 1%, or 0.5% agar having 80%, 75%, and 65% germination, respectively, for `Romance Scarlet' and 59%, 41%, and “24%, respectively, for `Showtime Blaze'.
Muskmelon (Cucumis melo L.) seed crops sometimes contain seeds with split coats that expand to twice their normal water content. These expanded seeds are often referred to as “fishmouth” seeds, because the split seed coat resembles an open fish's mouth when viewed longitudinally. “Fishmouth” seeds are dead seeds. However, little is known about why death occurs inside the fruit before harvest. Hermaphroditic flowers were tagged at anthesis and fruits were harvested at various intervals during the later stages of development and decay. Seeds were removed from the fruits and incubated in water on germination blotter paper for 14 days. The percentage of germinable, dead and “fishmouth” seeds were averaged for each Harvest date. Fruit pericarp samples were analyzed for pH, ethanol, and acetic acid content. At 50 days after anthesis (DAA), just past edible maturity, 100% of the seeds germinated. However, at 60 and 78 DAA germination dropped to 60 and 17%, respectively, while the occurrence of “fishmouth” seeds increased from 2 to 54% over the same period. The ethanol content of the tissue increased from 0.11 to 0.28%, the pH dropped from 6.2 to 5.1, and acetic acid concentration increased from 3.0 to 3.7 mM from 50 to 60 DAA, respectively. However, when dried seeds were incubated in the laboratory under conditions similar to those within the fruit, the formation of “fishmouth” seeds was related to the ageing effects of long term hydration and was not correlated with any chemical product within the fruit.
Seeds of two shrunken-2 (sh2) sweet corn (Zea mays L.) cultivars, Crisp N' Sweet 711 and How Sweet It Is were used to analyze seed quality factor differences between the cultivars. Negative correlations occurred among germination percentage and imbibition, electric conductivity, potassium concentration and total soluble sugars of the seed leachate. Imbibition and total soluble sugar in the leachate significantly increased as imbibition temperature increased from 5°C to 25°C in both cultivars. A significant increase in conductivity of the leachate also occurred in `Crisp N' Sweet 711' when temperature increased. Cracks in the seed coat were more frequent in `How Sweet It Is' than `Crisp N' Sweet 711'. The higher concentrations of soluble sugars in the seed, greater imbibition rate, leakage conductivity, potassium and sugar concentration in the leachate may have been directly related to the poorer seed quality of `How Sweet It Is'. The alteration in cell membrane structure caused by a rapid water uptake in `How Sweet It Is' may have led to the high concentration of electrolytes in the seed leachate. This, in turn, might provide a greater nutritive subtrate for fungi development.
Seeds (intact or slit) of lettuce (Luctuca sativa L.) cultivars with greater ability to produce ethylene germinated better under stressful conditions. Highly significant correlations were found between ethylene production and germination in 0.1 m NaCI (- 0.49 MPa) solution at 25C (r = 0.95, intact seeds), in - 0.3 MPa PEG solution (r = 0.86, intact seeds; r = 0.81, slit seeds), and in water at 32C (r = 0.80, slit seeds) or 35C (r = 0.80, slit seeds). Slitting the seed coat increased the ethylene production and improved germination during osmotic restraint in most cultivars, particularly in `Mesa 659' and `Super 59'. The differing ability of cultivars to produce ethylene during stress generally corresponded with their ability to generate germination potential. Ethylene production and germination potential in untreated and ACC-treated `Mesa 659' seeds increased upon slitting under stressful conditions. Thus, the ability of seeds to produce ethylene and to generate high germination potential under stressful conditions may be used as criteria to select stress-tolerant lettuce cultivars. Chemical names used: polyethylene glycol 8000 (PEG), 1-aminocyclopropane-1-carboxylic acid (ACC), (2-chlorethyl) phosphoric acid (ethephon).
Excluding seeded offspring at an early stage could be of great value to the breeder concerned with the development of seedless grapes (Vitis vinifera L.). We used the random amplified polymorphic DNA (RAPD) technique to identify molecular genetic markers, analyzing 82 individuals of a progeny resulting from a cross between `Early Muscat' (seeded) and `Flame Seedless'. Seven variables representing the traits of seedlessness were analyzed: mean fresh weight of one seed, total fresh weight of seeds per berry, perception of seed content, seed size categories evaluated visually, degree of hardness of the seed coat, degree of development of the endosperm, and degree of development of the embryo. Among 160 10mer primers, 110 gave distinct band patterns. Twelve markers yielded significant correlations with several subtraits of seedlessness, mainly with the mean fresh weight of one seed and the total fresh weight of seeds per berry. Multiple linear regression analysis resulted in high coefficients, such as R = 0.779 for fresh weight of seeds per berry, when the seven markers were included as independent variables in the model. Most of the seeded individuals, about 44% of the progeny, could be excluded using a two-step process of marker assisted selection.
The effects of pollination treatments on fruit set and five berry characteristics [mass, diameter, number of apparently viable seeds (well-developed, plump with dark seed coat), total seed number (includes apparently viable and partially developed seeds), and harvest date] were examined on three highbush blueberry cultivars. Pollination treatments included unpollinated, open pollinated, emasculated, and three hand pollinations that used pollen from the same flower, from the same cultivar, or from a different cultivar. Berries matured earliest and were smallest with the most apparently viable seeds in `Northland', `Patriot' had the greatest fruit set and smallest seed number, and `Bluecrop' matured the latest. Fruit set was greater, berry size larger, seed number smaller, and maturation later in 1990 than 1991. For all three cultivars, berries were generally smallest, latest maturing, and had the fewest seeds when pollination was prevented and were largest with the most seeds and earliest maturing in open visitation. Emasculation resulted in berries similar to those from unpollinated flowers. For berry characteristics, cross-pollination was of benefit for `Patriot' and possibly `Northland' but not `Bluecrop'. Thus, commercial highbush blueberry planting designs must be based on the pollination requirements of the particular cultivar. `Northland' berries almost always had seeds, while `Patriot' showed high levels and `Bluecrop' low levels of parthenocarpy.