Field experiments were conducted in 2000 and 2001 in Meridian, Calif. to evaluate the effects of cover crop mixtures and reduced tillage on yield, soil nitrogen (N), weed growth, and soil moisture content in organic processing tomato (Lycopersicum esculentum) production. The trial was set up as a randomized complete-block design with eight treatments consisting of a 2 × 3 (cover crop × tillage) factorial design, a fallow control (F) and a single strip-till (ST) treatment. Cover crop mixtures were either legumes (L), common vetch (Vicia sativa), field pea (Pisum sativum) and bell bean (Vicia faba), or those legumes with grasses (GL), annual ryegrass/triticale (Lolium multiflorum/xTriticosecale) in 2000; cereal rye (Secale cereale)/triticale in 2001. Tillage treatments included an incorporation of the cover crop at planting (IP), a delayed incorporation (DI) (17 to 19 days after planting), and no-till (NT). Due to regrowth of the annual ryegrass in 2000, tomato fruit yields in 2000 were reduced by 50% to 97% within all GL treatments. However, regrowth of the cover crop was not a problem in 2001 and yields were not different among treatments. Total percent weed cover was 1.6 to 12.5 times higher in NT than IP treatments in 2000 and 2.4 to 7.4 times higher in 2001 as weed pressure was mainly affected by tillage practices and less by cover crop type. In 2000, available soil N was 1.7 to 9.4 times higher in L than GL treatments and was significantly influenced by tillage, but there were no treatment effects in 2001 due to a 60% reduction in weed pressure and minimal or no cover crop regrowth. Soil moisture content did not differ between treatments in either year. These results demonstrate the importance of appropriate selection and termination of cover crops for their successful adoption in organic conservation tillage systems.
N.M. Madden, J.P. Mitchell, W.T. Lanini, M.D. Cahn, E.V. Herrero, S. Park, S.R. Temple, and M. Van Horn
Katy M. Rainey and Phillip D. Griffiths
The genetic basis for heat tolerance during reproductive development in snap bean was investigated in a heat-tolerant × heat-sensitive common bean cross. Parental, F1, F2, and backcross generations of a cross between the heat-tolerant snap bean breeding line `Cornell 503' and the heat-sensitive wax bean cultivar Majestic were grown in a high-temperature controlled environment (32 °C day/28 °C night), initiated prior to anthesis and continued through plant senescence. During flowering, individual plants of all generations were visually rated and scored for extent of abscission of reproductive organs. The distribution of abscission scores in segregating generations (F2 and backcrosses) indicated that a high rate of abscission in response to heat stress was controlled by a single recessive gene from `Majestic'. Abscission of reproductive organs is the primary determinant of yield under heat stress in many annual grain legumes; this is the first known report of single gene control of this reaction in common bean or similar legumes. Generation means analysis indicated that genetic variation among generations for pod number under heat stress was best explained by a six-parameter model that includes nonallelic interaction terms, perhaps the result of the hypothetical abscission gene interacting with other genes for pod number in the populations. A simple additive/dominance model accounted for genetic variance for seeds per pod. Dominance [h] and epistatic dominance × dominance [l] genetic parameters for yield components under high temperatures were the largest in magnitude. Results suggest `Cornell 503' can improve heat tolerance in sensitive cultivars, and heat tolerance in common bean may be influenced by major genes.
Gaétan Bourgeois, Sylvie Jenni, Hélène Laurence, and Nicolas Tremblay
producteurs de fruits et légumes transformés and the Centre de technologies en agroenvironnement for their financial contribution, as well as the field workers at the L'Acadie experimental farm for their help. The cost of publishing this paper was defrayed
D. Powell, R. Kelley, G. Yang, and M. Kamp-Glass
Alfalfa (Medicago sativa L.), one of the most important forage legumes in the United States, has been recognized as an aluminum-sensitive species (Kemp-Glass et al., 1993). Hematoxylin staining has been used to evaluate differences in root growth and stain uptake between sensitive and resistant individuals in wheat (Ruiz-Torres et al., 1992). Attention in this study is focused on the hematoxylin staining pattern because the procedure is simple and rapid. Ten alfalfa cultivars were used: `Apollo', `ARC', `Foundation Vemal', `Shenandoah', `Spreador 2', `WL 311', `Saranac', `Saranac AR', `Cimarron', and `Cimarron VR'. Twenty seeds of each were stained in a solution of hematoxylin for 2 days. After staining, the seedlings were transferred to a potting medium for 14 days. After 14 days, plantlets were transferred to Porters soil (pH 4.5, 80% aluminum saturation) and grown in the greenhouse for 60 days. After 60 days, fresh and dry root and shoot weights were taken. Root length densities were determined and these parameters were compared to the tolerance level predicted by hematoxylin stain. Results of stain correlate with biomass at highly significant levels and will be of great use in the development of an acid/aluminum-tolerant alfalfa.
C.O. Gwathmey and A. E. Hall
Removal of pods from legume crops may extend reproductive duration by delaying leaf senescence. In two years of field experiments, cowpea (Vigna unguiculata [L.] Walp. cv. CB5) pods were continuously harvested as they reached color–break or southernpea stage. The largely monocarpic reproductive pattern of non-picked CB5 was altered to a bimodal distribution by picking. During the first podding period, removal did not appreciably change reproductive duration nor the number of pods produced. It reduced dry weight in seed 22–34% and significantly delayed leaf senescence relative to the non–picked control. This increase in source:sink ratio was accompanied by increasing starch concentrations in stems and was followed by generation of a second set of pods which doubled the reproductive duration of picked plants. By contrast, starch reserves declined during the first podset in senescent control plants, which produced few pods thereafter. Picked plants produced 41–60% more pods/m2 over the entire season than non–picked CB5, but total dry weight in seed did not differ significantly since pod removal limited aced fill.
T.K. Hartz, P.R. Johnstone, E.M. Miyao, and R.M. Davis
Mustard (Brassica spp.) cover crop residue has been reported to have significant `biofumigant' action when incorporated into soil, potentially providing disease suppression and yield improvement for the succeeding crop. The effects of growing over-winter mustard cover crops preceding processing tomato (Lycopersicon escultentum Mill.) production were investigated in six field trials in the Sacramento Valley of California from 2002–04. A selection of mustard cover crops were compared to a legume cover crop mix, a fallow-bed treatment (the current grower practice in the region), and in two of the six trials, fumigation treatments using metam sodium. Mustard cover crops removed 115 to 350 kg·ha–1 N from the soil profile, reducing NO3-N leaching potential. Soil populations of Verticillium dahliae Kleb. and Fusarium spp. were unaffected by the cover crops, and there was no evidence of soilborne disease suppression on subsequent tomato crops. Mustard cover crops increased tomato yield in one field, and reduced yield in two fields. In one of two fields, metam sodium fumigation significantly increased tomato yield. We conclude that, while environmental benefits may be achieved, mustard cover cropping offers no immediate agronomic benefit for processing tomato production.
Hristina H. Stamenova-Berberova and Paul E. Read
Native plants are often ignored in horticulture because they may lack major ornamental traits and many of them are difficult to propagate. Creamy indigo (Baptisia bracteata Mnhl.) is a North American legume with considerable potential as a container-grown or ornamental plant for managed landscapes. Nodal explants from aseptically germinated seedlings were evaluated for axilary shoot and leaf development. The explants were cultured on Murashige and Skoog medium (MS) containing adenine sulfate at 80 mg•L-1, 30% sucrose, and different levels of N-6-benzyladenine (BA) (0.5,1.0,2.0 mg•L-1) supplemented with indole-3-acetic acid (IAA) (0.05, 0.1 or 0.5 mg•L-1) or with IAA omitted. Shoot regeneration occurred within 2 to 3 weeks. The best medium for shoot regeneration was MS supplemented with BA at 1.0 mg and IAA at 0.1 mg•L-1. Shoots were transferred onto rooting medium consisting of Ω MS supplemented with 1.0 mg alpha-naphthaleneacetic acid (NAA) and 1.0 mg indole-3-butyric acid (IBA)/L and 20% sucrose. Rooting took place within 3 to 5 weeks. Plantlets were then planted in soil mix, placed under a polyethylene tent for 2 weeks, and transferred into the greenhouse for further growth.
Jameel M. Al-Khayri, Teddy E. Morelock, and Edwin J. Anderson
Cowpea, or southernpea, is an important food legume that provides a source of high-quality protein, especially in the mature seeds. In the United States, industries exist to supply dry and processed seeds. Our aim is to develop a regeneration system for cowpea as a prerequisite for genetic engineering. Our objective was to examine the in vitro responses of shoot tips to growth regulators. Shoot tips isolated from in vitro-germinated seedlings (`Coronet') were cultured on MS medium containing 2,4-D at 0, 0.01, 0.1, or 1 mg·liter–1 and kinetin at 2.5, 5, 10, or 20 mg·liter–1. Cultures were maintained at 12-hour photoperiods and 24C. Callus, shoots, and roots or combinations thereof developed depending on the treatment. Callus formed on 1 mg 2,4-D/liter, regardless of the kinetin level, but at 0.1 mg 2,4-D/liter and 5 or 10 mg kinetin/liter, shoots also grew. Callus, shoots, and roots developed on 2,4-D lower than 0.1 mg·liter–1. Callus induced on 5 mg kinetin/liter and 0.01 mg 2,4-D/liter regenerated shoots on transfer to 5 mg kinetin/liter and 0.1 mg NAA/liter. This work may assist in the development of a micropropagation system for cowpea.
Fredrick A. Bliss
Fruits and vegetables are rich sources of the micro mineral elements and vitamins often lacking in diets based on cereals, grain legumes, and starchy roots and tubers, but void of animal products. When embarking on a breeding program to improve nutritional compounds, the way the fruit or vegetable is consumed in mixed diets must be considered. To alleviate nutritional problems, the nutrients must not only be present in the plant parts consumed, but also absorbed efficiently in the body. In some cases, it may be necessary to modify compounds to improve absorption as well as increase the concentration. Breeding to improve nutritionally related traits can be approached in a manner similar to that for other traits; i.e., identification of genetic variability, selection for enhanced levels using either individual phenotype or family mean values, and testing for field performance. In addition to improving amount and availability, avoidance of undesirable correlated responses due to genetic or physiological linkages between the trait of interest and other traits deleterious to either plant growth or the consumer is critically important during selection. The growing number of molecular marker-based linkage maps should prove especially useful for identifying genes of interest and employing marker-aided selection. When insufficient variability for amount or type of compound is present in the gene pool, strategies using transgenic plants may be useful.
G. Ghale, V.T. Sapra, C.A. Beyl, and C.B. Chawan
Soybean, Glycine max (L.) Merril is an annual self-pollinated diploid legume (sub-family Fabaceae). In the 1990s, soybean production in the far east, as in ancient times, was primarily for food consumption. Today, vegetable soybean is the dominant soyfood in Asia and is gaining popularity in the United States because of its versatility and nutrient value. Dozens of different forms of food have been developed from it. Tofu is one of the most important of these. Twenty four cultivars of vegetable soybean from two regional tofu tests (Alabama A&M and Virginia State Univ.) and 10 cultivars from the Alabama A&M Univ. soybean breeding project were evaluated for the physical and chemical characteristic of the resultant tofu. Data on protein, tofu yield, moisture content, tofu texture, and structure were recorded. Shear-force (used to evaluate texture) was determined with a Kramer Shear cell and micro-structure was examined using a scanning electron microscope. Seed protein content ranged from 30 to 54%. Tofu yield ranged from 41.9 to 83.0 g and texture of tofu ranged from 10 to 62.3 lb.