An efficient and reliable protocol of in vitro shoot regeneration must be first established to have a successful genetic transformation. As a member of legume family, alfalfa is very difficult for direct shoot regeneration. There is no published information on direct shoot organogenesis, although success has been well documented on embryogenesis, which must go through callus stage. Different plant growth regulators at various concentrations were evaluated for callus initiation, development, and direct shoot regeneration. Multiple shoots were produced directly from each individual explant. This will provide an efficient means for production of transgenic alfalfa plants. Therefore, genetic transformation of Medicago germplasm will be significantly expedited.
Guochen Yang and Marihelen Kamp-Glass
R.K. Striegler, M.A. Mayse, U. O'Keefe, and D.R. Wineman
Consumer concerns about pesticide residues and environmental degradation are having a significant impact on the California grape industry. Growers are using a variety of practices, from integrated pest management to certified organic production, to reduce the amount of pesticides and other synthetic inputs used in vineyards. This experiment was established to test selected sustainable cultural practices in a mature `Thompson Seedless' vineyard. Treatments included in the experiment were row middle management (cultivated vs. perennial legume cover crop) and nitrogen fertilization (compost vs. synthetic). Vine nutritional status, yield, fruit composition, pruning weight, and population levels of the variegated leafhopper were monitored each season (1992–1994). In addition, efforts were expanded during the 1994 season to include assessment of spider, herbivorous mite, and beneficial arthropod densities. Conventional cultural practices (cultivation and synthetic fertilizer) produced the highest yields during the 1992 and 1993 seasons. This result may have been due to the nutritional status of vines, which was generally better for the cultivation and synthetic fertilizer treatment, especially in 1992. In 1994, significant treatment effects on yield were not observed, indicating that legume cover crop plots had become fully established. Sustainable cultural practices had little impact on growth, fruit composition, or insect pest pressure. `Thompson Seedless' grapes were grown for three seasons without the use of insecticides or herbicides. Vine diseases were managed by cultural practices and application of sulfur.
Wayne F. Whitehead and Bharat P. Singh
The objective of this study was to determine if winter legume or grain cover could support net photosynthesis (Pn) and plant dry matter production comparable to recommended rate of synthetic N. The following winter/spring fertility treatments were applied: 1) 0 N winter/0 N spring, 2) 0 N winter/90 kg·ha–1 N spring, 3) 0 N winter/180 kg·ha–1 N spring, 4) 0 N winter+abruzi rye/0 N spring, 5) 0 N winter+hairy vetch/0 N spring, and 6) 0 N winter+crimson clover/0 N spring. `Mountain Pride' tomato was planted in all plots in spring. Plant dry weight and Pn were measured at flowering, fruiting and prior to senescence. The highest Pn (22.78 μmol CO2/m2 per s) and leaf dry weight (115.2 g/plant) were obtained at fruiting, while highest branch dry weight (194.5 g/plant) occurred prior to senescence. There was significant increase in plant dry weight during reproductive growth phase. Tomato plants receiving supplemental N from crimson clover or hairy vetch had Pn and plant dry weight comparable to those receiving synthetic N. The results of this study indicated that legume cover crops were as effective as commercial N fertilizer for supporting photosynthesis and vegetative growth of tomato.
G.D. Hoyt and J.F. Walgenbach
Conservation tillage systems provide optimum conditions to reduce soil erosion and increase surface soil organic matter. This experiment was established with the long-term goal of developing conservation tillage systems that use either chemical inputs to produce vegetables and control pests, or legume cover crops, biological pesticides, and tillage to provide plant nutrition and control pests. The experiment consisted of cabbage (Brassica oleracea var. L. Capitata Group) grown by traditional-tillage (TT) or strip-tillage (ST) culture using either chemical or organic production methods for pest control. Cabbage heads were heavier with TT than with ST for the chemical production system. Although weed biomass was significantly higher with organic methods, there was a poor relationship between weed biomass at harvest and cabbage head weight. The lack of differences in lepidopterous pest damage suggests that the conservation tillage systems examined likely would not affect lepidopterous pest management systems using biological insecticides. Within tillage treatments, the organic production system resulted in less Alternaria infection than did the chemical production system. Since no fungicides were applied on any treatment, lower disease ratings in the organic production system may have been the result of reduced soil contact of the cabbage leaves from the increased soil coverage by the weed and intercropped legume canopy.
Nancy G. Creamer
Five grasses, six broadleaf species, and five legume/grass mixtures were evaluated for their production of aboveground biomass (AGB), nitrogen contribution, C: N ratio, ability to compete with weeds, and susceptibility to three methods of mechanical kill. Of the legume species, sesbania, cowpea, and soybean produced the most biomass, which totaled 5542, 4227, and 3934 kg·ha–1, respectively. Nitrogen in the AGB of these species was 109, 95, and 83 kg·ha–1, respectively. AGB production of the grass species ranged from 8677 kg·ha–1 for sorghum–sudangrass to 5247 kg·ha–1 for pearl millet. Nitrogen in the AGB for the grass species ranged from 68 to 38 kg·ha–1. In general, the cover crops most competitive with weeds were those that had an excess of 3900 kg AGB/ha. The broadleaf species were effectively controlled by mowing, while undercutting controlled five of the species, and rolling provided little control. Undercutting provided the best control of the grasses, while rolling was effective on the most mature species, and mowing provided little control.
Francis X. Mangan and Stephen J. Herbert
Field research was conducted in Deerfield, Mass. to study the effects of leguminous cover crops on sweet corn yield. Oat was planted alone and in combination with four leguminous cover crops August 8, 1990. Cover crop residue was disked once and sweet corn seeded April 23, 1991. Each cover crop combination had three rates of nitrogen added in two applications. Sweet corn seeded into stands of hairy vetch (Vicia villosa) yielded the highest of the cover crop combinations. All leguminous cover crop treatments yielded higher than oat alone or no cover crop when no synthetic nitrogen was added. Cover crop combinations were seeded again in the same field plots August 12, 1991. Oat biomass in November was greater where there had been leguminous cover crops or high rates of synthetic nitrogen. Legume growth was retarded in the plots that had previously received high nitrogen. It is thought that legume growth was reduced in the high nitrogen treatments due to increased oat growth and higher soil nitrogen levels which could inhibit root nodulation.
P. R. Johnstone, T. K. Hartz, E. M. Miyao, and R. M. Davis
Mustard cover crop residue has been reported to have a “biofumigant” action when incorporated into the soil, potentially providing significant disease suppression and yield improvement for the succeeding crop. Such activity could be particularly useful in processing tomato rotations, where consecutive cropping invariably results in yield decline. Agronomic and environmental effects of growing over-winter mustard cover crops preceding tomato production were investigated in three field trials between 2002 and 2004. Two mustard cover crops [`Pacific Gold', a brown mustard (Brassica juncea), and `Caliente', a blend of brown and white mustard (Sinapis alba)] were compared to a legume cover crop mix, a fallow bed treatment (the standard grower practice in this region), and, in two of the three trials, a fumigation treatment using metam sodium. No suppression of soil populations of Verticillium dahliae or Fusarium spp. was observed with the mustard cover crops, nor was there any visual evidence of disease suppression on subsequent tomato crops. In these fields, the mustard either had no effect, or reduced tomato yield, when compared to the fallow treatment. At one of two sites, metam sodium fumigation significantly increased tomato yield. The presence of a cover crop, whether mustard or legume, reduced winter runoff by an average of 50% over two years of trials. No benefit of mustard cover cropping beyond this reduction in winter runoff was observed.
Sylvie Jenni, Gaétan Bourgeois, Hélène Laurence, Geneviève Roy, and Nicolas Tremblay
We thank Lucette LaFlamme for her technical assistance, the Quebec Food Processors Association, the Fédération québécoise des producteurs de fruits et légumes de transformation, and the Centre de technologies en agroenvironnement for their
J. Yu, W.K. Gu, R. Provvidenti, and N.F. Weeden
1 Dept. of Horticultural Sciences. 2 Dept. of Plant Pathology. This work was supported in part by a grant from the Cool Season Food Legume Program, administered by the Univ. of Idaho, Moscow. The cost of publishing this paper was defrayed in part by
M.C. Scott, G. Caetano-Anollés, and R.N. Trigiano
1 Plant Molecular Genetics, Institute of Agriculture and Center for Legume Research, The University of Tennessee, Knoxville, TN 37901-1071. 2 To whom reprint requests should be addressed. We thank Yoder Brothers, Inc., for donating the plant