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Main conclusion Enhanced levels of indole-3-acetic and raised auxin to cytokinin ratios in the stem base contribute to the positive acropetal gradient in rooting capacity of leafy single-node stem cuttings of rose. Abstract Cuttings excised from different nodal positions in stock plants can differ in subsequent adventitious root formation. We investigated the involvement of the auxin–cytokinin balance in position-affected rooting of Rosa hybrida. Leafy single-node stem cuttings of two rose cultivars were excised from top versus bottom positions. Concentrations of IAA and cytokinins were monitored in the bud region and the stem base during 8 days after planting using chromatography–MS/MS technology. The effects of nodal position and external supply of indole-butyric acid on rooting were analyzed. Most cytokinins increased particularly in the bud region and peaked at day two before the bud break was recorded. IAA increased in both tissues between day one and day eight. Top versus bottom cuttings revealed higher levels of isopentenyladenosine (IPR) in both tissues as well as higher concentrations of IAA and a higher ratio of IAA to cytokinins particularly in the stem base. The dynamic of hormones and correlation analysis indicated that the higher IPR contributed to the enhanced IAA in the bud region which served as auxin source for the auxin homeostasis in the stem base, where IAA determined the auxin–cytokinin balance. Bottom versus top cuttings produced lower numbers and lengths of roots, whereas this deficit was counterbalanced by auxin application. Further considering other studies of rose, it is concluded that cytokinin-, sucrose- and zinc-dependent auxin biosynthesis in the outgrowing buds is an important factor that contributes to the enhanced IAA levels and auxin/cytokinin ratios in the stem base of apical cuttings, promoting root induction.

Prolonged moisture stress and high vapour pressure deficits reduced the shoot water potential, shoot population density, rate of shoot extension and yield of clonal tea. The more drought susceptible Clone 6/8 had a lower shoot water potential, rate of shoot extension, number of shoots per unit area, rate of shoot regeneration and yield than the more tolerant Clones 31/8,57/ 15 and 15/10 during the periods of low soil moisture, which coincided with high vapour pressure deficits. The changes in the shoot growth components could be used as an index of the suitability of different clones for different regimes of soil moisture and vapour pressure deficits.Factores ambientales que afectan el rendimiento del te RESUMEN La prolongada falta de humedad y deficiencias en la alta presion de vapor reducen el potencial de agua del brote, la densidad de la poblacion de brotes, el indice de extension de brotes, y el rendimiento del te clonal. La clona mas susceptible a la sequia, la 6/8, presento un menor potencial de agua, menor indice de extension de brotes, menor cantidad de brotes por superficie de unidad, menor indice de regeneration de brotes, y menor rendimiento que las donas mas tolerantes -31/8, 57/15 y 15/10-durante los penodos de baja humedad del suelo, lo cual coincidio con las deficiencias en alta presion de vapor. Los cambios en los componentes del crecimiento de brote podrian utilizarse como indice de la adecuacion de las diversas clonas a los diferentes regfmenes de humedad del suelo y deficiencias de presion de vapor.

Forty-eight inbred lines of maize with varying levels of resistance to gray leaf spot (GLS) were artificially inoculated with Cercospora zeina and evaluated to characterize partial disease resistance in maize under field conditions from 2012 to 2014 across 12 environments in western Kenya. Eight measures of disease epidemic—that is, final percent diseased leaf area (FPDLA), standardized area under the disease progress curve (SAUDPC), weighted mean absolute rate of disease increase (ρ), disease severity scale (CDSG), percent diseased leaf area at the inflection point (PDLAIP), SAUDPC at the inflection point (SAUDPCIP), time from inoculation to transition of disease progress from the increasing to the decreasing phase of epidemic increase (TIP), and latent period (LP)—were examined. Inbred lines significantly (P < 0.05) affected all measures of disease epidemic except ρ. However, the proportion of the variation attributed to the analysis of variance model was most strongly associated with SAUDPC (R2 = 89.4%). Inbred lines were also most consistently ranked for disease resistance based on SAUDPC. Although SAUDPC was deemed the most useful variable for quantifying partial resistance in the test genotypes, the proportion of the variation in SAUDPC in each plot was most strongly (R2 = 93.9%) explained by disease ratings taken between the VT and R4 stages of plant development. Individual disease ratings at the R4 stage of plant development were nearly as effective as SAUDPC in discerning the differential reaction of test genotypes. Thus, GLS rankings of inbred lines based on disease ratings at these plant developmental stages should be useful in prebreeding nurseries and preliminary evaluation trials involving large germplasm populations.

Detailed germination studies were conducted on seeds of two subspecies of Vernonia. galamensis (nairobiensis and afromontana var. gibbosa), a potential industrial oil crop. Plants of both subspecies were grown at two experimental sites in Kenya and sequential harvesting carried out during seed development to determine the best production environment and optimum harvest time for lowdormant, high-quality seed-lots. Seeds harvested at different maturity levels were germinated under different temperature regimes before and after desiccation. The studies revealed that the onset of germinability and desiccation tolerance was achieved during the dry matter accumulation phase of seed development and that seeds developed dormancy 3 to 6 d after acquiring germinability, with high levels of germination only reaching under an alternating temperature regime. The seeds of the subsp. nairobiensis were shown to be more dormant than those of the subsp. afromontana var. gibbosa. Similarly, seeds harvested from a warmer environment were less dormant than those from a cooler environment.