Many developing countries lack the facilities to produce and distribute high quality rhizobia inoculants for farmers who are interested in planting soybeans [Glycine max (L.) Merr.]. If soybean varieties were available that could nodulate effectively with the ubiquitous, cowpea‐type rhizobia, farmers could successfully grow soybeans without inoculation or fertilizer N. When 400 diverse soybean lines were tested at five sites in Nigeria for the ability to nodulate with indigenous rhizobia, only 10 were highly promiscuous, that is, capable of forming an effective symbiosis at all sites. Some entries were rated as compatible with indigenous rhizobia at one or two sites but failed to nodulate profusely at the other locations. Twenty‐two isolates from nodules collected from profusely nodulated soybean plants and three other isolates prepared from cowpea nodules, were used to inoculate the 10 most compatible selections from the previous trial and two U.S. varieties, ‘Bossier’ and TGm 294. ‘Malayan’, a local Nigerian cultivar, formed an effective symbiosis with 21 of 22 soybean isolates; nodule and shoot weights in each case being greater than or equal to inoculation with Nitragin multistrain inoculant. Other accessions that displayed high degrees of promiscuity were M‐381, TGm 120, TGm 119, Indo 180, and Indo 243. Whereas, Bossier formed an effective symbiosis with only one of the isolates, and TGm 294 was compatible with only 2 of the 22 rhizobia isolates. The promiscuously nodulating soybeans identified in the screening trial were also compatible with at least two of the three cowpea isolates, but Bossier and TGm 294 were compatible with none of them. When the scion of Bossier on ‘Jupiter’ (both of which have high yield potential) was grafted onto the root stocks of ‘Orba’ or Malayan (Promiscuous nodulators) enough N was fixed to meet the requirements of high yielding genotypes. These results indicate that by genetically incorporating promiscuity into varieties with high yield potential one would not necessarily reduce yield potential.
The effect of inoculation with R. japonicum on nodulation, plant growth, and yield of diverse soybean [Glycine max (L.) Merr.] cultivars was studied in Nigeria and Tanzania. Experiments were conducted on soils not previously cropped with soybean. Local cultivars from Nigeria and Indonesia nodulated with indigenous Rhizobium spp. at two sites in Nigeria. Inoculation with several strains of R. japonicum occasionally increased nodule mass of the local cultivars but seldom plant growth or yield. In contrast, U.S. bred cultivars nodulated poorly without inoculation. Large increases in growth and yield were obtained when the U.S. cultivars were inoculated. Similarly, cultivars bred and selected in Tanzania were compatible with native Rhizobium spp.; whereas Bossier (U.S. origin) did not nodulate unless inoculated. The local cultivars used in these experiments were promiscuous and recognized Rhizobium ssp. that were ineffective on U.S. bred material. However, the local cultivars have low yield potentials due to poor agronomic characters. In contrast, the cultivars of U.S. origin are agronomically superior but require inoculation with R. japonicum to realize their yield potential. A breeding program based upon transferring the promiscuous character of some local cultivars to improved U.S. material could produce varieties that do not require inoculation with R. japonicum and still produce high yield.
Application of 10-8M 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) to the roots of 10-day old barley (Hordeum vulgareL. ‘Coho’) seedlings grown in nutrient cultures increased the water-soluble protein content when grown at 20 C day, 15 C night with 3 mM nitrate nitrogen. The water-soluble carbohydrate content decreased with increases in water-soluble protein. In a time-course study simazine increased14C-leucine incorporation into protein prior to increasing nitrate uptake, indicating that simazine may have a direct influence on protein synthesis. The nonherbicidal metabolite of simazine, 2-hydroxy-4,6-bis(ethylamino)-s-triazine (hydroxysimazine), did not affect14C-leucine incorporation into protein.
This paper reports the effectiveness of plastic shelters in overcoming soil-related and biotic constraints to vegetable production in Belize, Central America, where rainy-season tomatoes and sweet peppers are almost totally destroyed by geminiviruses. Use of pesticides is rampant, while rapid decline in soil productivity induces farmers to abandon previously used lands and clear new lands from virgin forests. We postulated that plants growing in the open-field environment are infected early by the soil-borne pathogens deposited on the plants from clouds of fine soil particles arising from the soil splash Lalit M. Arya and Edward L. Pulver are affiliated with the Winrock International Institute for Agricultural Development, 38 Winrock Drive, Morrilton, AR 72110-9537. M. Th. van Genuchten is affiliated with the U.during high-intensity rainfall. The products of fungal and bacterial decay attract white flies (the vector for geminiviruses) and plants already weakened by the infection succumb easily to the viruses. A production system in which plant and soil surfaces are protected from direct rainfall using plastic shelters, was designed and field tested with tomatoes and sweet peppers. On average, plastic shelters increased tomato and sweet pepper yields by 169% and 96%, respectively, without any use of pesticides. Weed growth under the shelter was negligible, and plants maintained greenness and production well into the fourth month after transplanting. In contrast, open-field plots were infested with weeds, and plants were completely destroyed by the middle of the third month. The number of white flies visiting the plastic-shelter plants was only about 28% of that in the open-field. We conclude that total protection of soil and plant surfaces from rainfall is the most effective plant protection measure. The proposed system uses small land area on a continuous basis, provides stable production, requires little or no plant protection chemicals, and raises farmer income.
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