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Suboptimal temperatures cause grain yield reductions generally associated with low seed-set in sorghum [Sorghum bicolor (L.) Moench]. Low proline concentration in pollen has been associated with cold-induced male sterility. This study was done to (i) determine free proline concentrations in grain sorghum pollen after low temperature exposure, (ii) determine the relationship between seed-set and proline concentration in pollen, and (iii) determine the association of proline concentration in pollen with grain yield in sorghums of different maturity. Eleven sorghum genotypes, grown in a greenhouse at 27/22 °C (day/night) until the early boot stage were transferred to 20/10 °C in growth chamber until physiological maturity. Concentration of proline in pollen was determined at anthesis and related to seed number and grain yield. Proline concentrations in pollen increased from 19 to 36 μg∙mg−1 fresh wt. to 30 to 49 μg∙mg−1 fresh wt. at low temperatures. Seed number and grain yield were reduced by low temperature in most of the genotypes. Percent seed-set in male sterile lines was significantly correlated (r = 0.45**) with free proline concentrations in the pollen from 13 fertile hybrids grown under cold or control conditions. Higher concentrations of proline in pollen under cool and also control temperatures seemingly contribute to greater pollen viability in grain sorghum. In 21 sorghum hybrids grown under control temperatures, seed number per panicle was found correlated (r = 0.42*) to free proline concentrations in pollen. Genotypic differences in pollen proline concentration were not associated with differences between maturity groups. Keywords: Sorghum bicolor (L.) Moench, pollen, free proline, low temperatures, seed-set, grain yield.

Previous studies have demonstrated that pollen of sorghum [Sorghum bicolor (L.) Moench] loses capacity to both germinate in vitro and to set seed in vivo soon after being shed. The current study evaluates the capacity for dehydrated pollen to effect in vitro germination, reduce tetrazolium chloride, and set seed on cytoplasmic male sterile plants. Morphological changes during pollen germination were examined by scanning electron microscopy (SEM). Close to 70% of the pollen germinated in 5 min, or less, when collected at 80% relative humidity (RH) and stored in sealed glass vials. Pollen tubes elongated autotropically with atmospheric humidity apparently being a controlling factor in the process. Pollen dehydrated at 50% RH and 25°C for 15-30 min neither germinated in vitro, reduced tetrazolium chloride, nor set seed on male sterile plants. Rehydrating the pollen did not restore the capacity for germination. SEM micrographs demonstrated that elongating pollen tubes encircled the pollen grain and were contiguous to the surface. A fibrillar-like material existed on the exine of separated pollen grains at the point where the grains had been previously attached.

Juvenile plants of Thymus mastichina, Thymus zygis, Lavandula pedunculata, Genista hirsuta, and Cistus ladanifer were transplanted from the field to the greenhouse; the soil used was the same in which they had grown at their natural site. The plants were grown to maturity to determine comparative growth, water status, and mycorrhizal colonization under greenhouse conditions and to determine the influence of drought on the symbiosis. After 24 months, L. pedunculata showed the most developed root system; G. hirsuta showed the lowest root/shoot ratio and the lowest percentage of mycorrhizal colonization. This percentage ranged from 32.0% to 82.4% for G. hirsuta and L. pedunculata, respectively. There was a positive relationship between root biomass and root/shoot ratio with mycorrhization percentage, and a positive response of water potential to that percentage also occurred. After a moderate drought treatment over 4 weeks, root and shoot biomass and root/shoot ratio as well as mycorrhizal colonization decre...