. Furthermore, few studies of abiotic stress resistance have been reported. A thorough study of drought responses of six apple species, including M . sieversii , was reported by Jinghui et al. (1996) . Based on leaf area index, stomata density, osmotic
Determination of ploidy is an essential plant breeding technique. Laboratory exercises for teaching students how to determine ploidy in plant tissues using various techniques are described for geranium and onion. The different methods include root tip squashes, pollen mother cell squashes, pollen grain size and germinal pore counts, stomata size and density determination, and gross morphology.
morphological characteristics such as stomata density and leaf curvature influence infection of P. belbahrii in different Ocimum species, and if so, could be effective visual markers for screening in plant breeding. The large morphological variations in the
Selected physiological and anatomical characteristics of four chilling-tolerant sweetpotato genotypes were evaluated. Although the genotypes were considered highly tolerant to chilling, it was proposed that differences in their mechanism for tolerance existed. A genotype temperature interaction for chlorophyll fluorescence ratio was observed when the plants were exposed to 5 °C. Genotype differences were found for electrolyte leakage and peroxidase activity. There were no differences found for fatty acid percentage composition of the glycolipid or the phospholipid fraction from leaf samples. There were no differences in diffusive resistance and transpiration rate among the genotypes; however, stomata density, leaf shrinkage, and specific leaf weight differed among the genotypes. Differences were also found among the genotypes for percent leaf dry weight, leaf thickness, and cellular structure of the leaf. It was concluded that the basis or mechanism for chilling tolerance was not the same for the four genotypes tested; therefore, combining traits for tolerance could lead to higher tolerance levels.
Plasmopara viticola infects and sporulates through stomata of susceptible grape leaves. Sporulation, chlorosis, and necrosis ratings were made in 1994 and 1995 on grape selections and cultivars and Vitis species grown in a fungicide-free vineyard. Cellulose-acetate impressions were made of the abaxial leaf surfaces and stomata were carefully counted within a circle 100 μm in diameter under a light microscope. Leaves were rated as either pubescent or glabrous. There were significant differences among genotypes for sporulation, chlorosis, and necrosis for 1994 and 1995, with highly significant correlations over both years. Stomatal densities were significantly different, but there were no correlations among levels of downy mildew and stomata! densities. Pubescent leaves had significantly higher sporulation, chlorosis, and necrosis ratings for downy mildew than glabrous leaves over both years.
Pod stomatal density and Ca concentration levels were analyzed for six commercial snap bean cultivars harvested at four planting dates in an attempt to find morphological traits that are related to cultivar differences in pod Ca concentration. The experimental layout was a randomized complete-block design with two replications per planting date, all grown in one location. Snap beans were planted at 1 week intervals beginning 9 June 9 1995 and were harvested in August. Sampling consisted of five pod sizes (1, 2, 3, 4, and 5 according to commercial standards) from each genotype. Stomatal countings were performed using a microscope linked to a television camera. Determinations for pod Ca concentration were made using an atomic absorption spectrophotometer. No differences were detected for pod Ca concentration among planting dates, although there were differences for pod Ca concentration and stomata density among cultivars. Pod stomatal density was positively correlated to pod Ca concentration (R 2 = 0.60), while pod maturity appeared to be negatively correlated to pod Ca concentration (R 2 = 0.37) and pod stomatal density (R 2 = 0.49).
The effects of leaf age, guttation, stomata and hydathode characteristics, and wounding on the symptom development of gummy stem blight [Didymella bryoniae (Auersw.) Rehm] of cucumber (Cucumis sativus L.) were studied to develop a useful germplasm screening method. Older cucumber leaves were more susceptible than younger leaves in field, greenhouse, and detached-leaf tests. Compared to seedlings with true leaves, seedlings at the cotyledon stage were less susceptible, had a smaller variance for ratings, and were more likely to escape infection. Stomata density and hydathode counts were not correlated with field ratings; but, stomata length on older leaves was highly correlated with susceptibility y. In greenhouse and field tests, susceptibility y increased as guttation increased and actively guttating plants were more susceptible than nonguttating plants. Phylloplane moisture and/or nutrition were more important in the infection process than was stomata] opening. Although important, guttation was not necessary for infection. Dawn inoculation of field or greenhouse tests increased leaf symptoms compared with dusk inoculation. The increase was likely due to the free water and nutrients provided by guttation. Genotype ranks and ratings for detached-leaf tests were not correlated with field results. A useful method, highly correlated (r = 0.82 to 0.96) with field ratings. for screening germplasm in the greenhouse was developed.
present in a 0.04-mm 2 area of leaf was counted. Stomata density was calculated by dividing the number of stomata by 0.04. Data were subjected to ANOVA (Proc GLM) using SAS (version 9.4; SAS Institute). Mean separation using Tukey’s honestly significant
accession. Five fields of view were observed for each leaf to estimate the stomata density (no./mm 2 ). Stomata length and width were measured on three leaves per accession and 10 stomata per leaf using ImageJ (version 1.53e; National Institutes of Health
in a similar stomata size as the control. Heat preconditioning had no effect on stomata density of either cultivars. In both the cultivars, stomata density was significantly greater at higher challenging temperature 35 °C day/28 °C night with and