Soybean [Glycine max (L.) Merr.] is sensitive to chilling temperatures (≈ 15°C) at flowering resulting in reduced seed yield and physical quality (brown pigmentation near the hilum region). In Japan, soybean cultivars with yellow hilum color are preferred to those with brown hilum color. However, of the two, the genotypes with yellow hilum are more sensitive to chilling temperatures. Because a combination between brown pubescence and yellow hilum cause a discoloration of the seed coats, in northern Japan, all genotypes with yellow hilum have gray pubescence. This study was conducted to determine if pubescence color, controlled by gene T/t, was related to chilling tolerance in a pair of soybean lines near‐isogenic for gene T/t and if the near‐isogenic lines differed for N2‐fixing ability under chilling conditions. Two determinate near‐isogenic lines for gene T/t, To7B with allele T (brown pubescence and brown hilum) and To7G with allele t (gray pubescence and buff hilum), were exposed to 15°C (day/night) in a phytotron at flowering. Seed coat pigmentation was scored by exposing plants to 15°C for 2 wk beginning at 8 d after anthesis. Plant height, acetylene‐reducing activity (nitrogenase activity), maturity date, and seed yield were compared by exposing plants to ]15°C for 4 wk beginning at anthesis. Under control conditions, only plant height was different between the lines. By exposing plants to 15°C, seed coat pigmentation near the hilum region increased with the age of flowers at the time of chilling treatment in To7G. No pigmentation was observed in the seeds of To7B. Nitrogenase activity and seed yield were less and maturity date was later in To7G than To7B only under chilling treatment. These results suggest that allele T is associated with chilling tolerance due to either pleiotropy or close linkage.

To identify differences in root plasticity patterns of two upland New Rice for Africa (NERICA) varieties, NERICA 1 and 4, in response to drought under conditions with contrasting soil profile characteristics, soil moisture gradients were imposed using a sloping bed system with depths ranging 30-65 cm and a line-source sprinkler system with a uniformly shallow soil layer of 20 cm depth. Varietal differences in shoot and root growths were identified only under moderate drought conditions, 11-18% v/v soil moisture content. Further, under moderate drought soil conditions where roots could penetrate into the deep soil layer, deep root development was greater in NERICA 4 than in NERICA 1, which contributed to maintaining dry matter production. However, under soil conditions with underground impediment to deep root development, higher shoot dry weight was noted for NERICA 1 than for NERICA 4 at 11-18% v/v soil moisture content, which was attributed to increased lateral root development in the shallow soil layer in NERICA 1. Enhanced lateral root development in the 0-20-cm soil layer was identified in NERICA 1 even under soil conditions without an impediment to deep root development; however, this did not contribute to maintaining dry matter production in upland rice. Thus, we show different root developmental traits associated with drought avoidance in the two NERICA varieties, and that desirable root traits for upland rice cultivation vary depending on the target soil environment, such as the distribution of soil moisture and root penetration resistance.

An agar plate method has been developed for the rapid, preliminary screening of large numbers of rhizobia for tolerance to acidity and aluminum (acid-Al). Media containing pH indicators are used, and distinguish true tolerance from cases where growth depends on a previous pH shift. Strains which were highly tolerant or sensitive to acid Al on agar behaved similarly in defined liquid media. Strains that formed dry, pinpoint colonies were more sensitive to acid-AI than those that formed large, gummy colonies.Additional Index Words. acidity, aluminum, cowpea rhizobia, pH indicators, Rhizobium japonicum.Ayanaba, A., S. Asanuma, and D.N. Munns. 1983. An agar plate method for rapid screening of Rhizobium for tolerance to acid-aluminum stress. Soil Sci. Soc. Am. J. 47:256-258.METHODS have been developed recently for the preselection of Rhizobium strains tolerant of the soil acidity factors: aluminum, phosphate, and acidity (Date and Halliday, 1978;Keyser and Munns, 1979) and so of possible value as inoculant strains in the tropics. In these studies test strains are added to the stress media, incubated, and then examined for turbidity. In more refined tests, incubated cultures are monitored for cell multiplication prior to detectable pH changes.Screening for tolerance of acidity and Al can be vitiated by shifts in pH, which rhizobia sometimes induce depending on the buffering and particular composition of the medium (Date and Halliday, 1978). In agar media, local neutralization at the point of inoculation could become specially important, especially with large inocula. We report on an agar plate method that permits rapid screening of large numbers of rhizobia for tolerance to

New Rice for Africa (NERICA) is a general name for interspecific rice varieties derived from a cross between the high-yielding Asian rice (Oryza sativa L.) between locally adapted African rice (Oryza glaberrima Steud.). Eight NERICAs were evaluated for cold tolerance (CT) at the reproductive stage and compared with their O. sativa parents and three Japanese standard rice varieties over 3 years. Cold tolerance was evaluated based on the filled grain ratio (FGR) after cold water irrigation. The FGR was greatly reduced by cold water irrigation. NERICA 1, 2 and 7 had higher FGR (51.9-57.9 %), while NERICA 6, 15 and 16 had lower FGR (6.2-14.5 %). NERICA 1, 2 and 7 were less affected by cold stress, with a 31 % mean reduction in FGR, while NERICA 6, 15 and 16 were greatly affected, with their FGRs being reduced by more than 80 %. NERICA 3 and 4 were moderately affected by cold stress, with about 45 % reduction rate in FGR. FGR significantly influenced the grain weights of the varieties with strong positive correlations (r = 0.83-0.91; P < 0.001), and thus, similar trends in grain weights were observed. Grain weights were reduced by 61.7-96.4 % under cold stress. NERICA 1, 2 and 7 showed significantly better performance than NERICA 3 and 4, while NERICA 6, 15 and 16 performed poorly under cold water irrigation. The Japanese varieties Koshihikari (very tolerant) and Ozora (moderately tolerant) were more affected by cold water irrigation than NERICA 1, 2 and 7. On the basis of the mean reduction rate (%) in FGR under cold stress, the varieties were classified as follows: NERICA 1, 2 and 7 as tolerant; NERICA 3 and 4 as moderately tolerant; and NERICA 6, 15 and 16 as susceptible to cold stress. However, NERI-CA 7 grain yields were lower under cold stress due to both greatly reduced number of panicles per plant and number of spikelets per panicle. Therefore, NERICA 1 and 2 are suitable candidates for production in the highland regions of East Africa and should be promoted for production.

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