Significant Cultivar Differences Research Articles

Sugarcane cultivar genetic gains for coastal agro-ecological regions of South Africa

Cultivar genetic gains quantify the increase in productivity from release of cultivars and measure genetic improvements from plant breeding. The objectives of this study were to evaluate the genetic gains from sugarcane coastal cultivars and evaluate their contribution to productivity. Data were derived from replicated plant breeding and post-release variety evaluation trials conducted by the South Africa Sugarcane Research Institute (SASRI) from 1996 to 2020. There were significant cultivar differences for cane yield, sucrose content, sugar yield, fibre % and purity %. Significant analyses of cultivar by location, cultivar by crop-year and cultivar by location by crop-year indicate further optimisation of cultivar disposition is needed to increase productivity. Cultivar genetic gains were found for cane yield (0.19–0.48 t ha−1), sucrose content (0.01–0.02%), sugar yield (0.03–0.07 t ha−1 per year), fibre % cane (0.04–0.06%) and purity % (0.02–0.04%), highlighting the increased yield and quality from genetic improvement. The best cultivars produced 8–22% higher sugar yields than popular cultivars indicating that planting high yield cultivars did increase yields. Sugar cane production declined at a slower rate than area planted, also showing the benefit of high yield cultivars. Increasing the area planted to new, higher yielding cultivars will increase sugar yields for coastal regions of South Africa.

Intercellular void space effects on Kentucky bluegrass traffic tolerance

AbstractAthletic field safety is a top concern of field managers and athletic directors across all sports. Increased field usage on fields with traffic‐sensitive cultivars results in reduced turf cover and therefore decreased field safety. Kentucky bluegrass (Poa pratensis L., KBG) is the most widely used cool‐season turfgrass on athletic fields due to its dense turf canopy. While most KBG cultivars have strong recuperative potential, significant cultivar differences in ability to withstand athletic field traffic exist. This study was conducted to determine whether leaf epidermal cell sizes predict differences in KBG cultivar traffic tolerance. Upper epidermal cell size, lower epidermal cell size, and intercellular void space (IVS) were measured on three traffic‐tolerant and three traffic‐sensitive KBG cultivars from the 2011 National Turfgrass Evaluation Program KBG trial, arranged in a randomized complete block design with three replications. Transverse sections of leaf tissue were fixed in an acid/alcohol solution and embedded with paraffin prior to sectioning for imaging by light microscopy. Cell size was determined by counting cells per unit area from light microscopy images. Leaf upper and lower epidermal cell size was not a predictor of traffic tolerance. Differences were measured in IVS at the cultivar level and at the traffic‐sensitive vs. traffic‐tolerant grouping contrast level. Traffic‐tolerant cultivars exhibited larger IVS (2823 μm2) than traffic‐sensitive cultivars (1112 μm2). Further investigation of these leaf anatomy size theories in relation to athletic traffic tolerance should be conducted on more cultivars, including recently released commercially available genotypes.

Solvent retention capacity and swelling index of glutenin in hard red wheat flour as possible indicators of rheological and baking quality characteristics

To overcome the cost and expense of milling and baking hundreds of samples in wheat breeding programs, cereal chemists have developed various rapid predictive tests for end-use quality assessment. In this study, five small-scale rapid tests, including Solvent Retention Capacity (SRC) and Swelling Index of Glutenin (SIG), were compared for viability and accuracy to determine end-use quality using small quantities of flour. The tests were applied on commercial hard red spring and hard red winter wheat cultivars from two of the three main production regions in South Africa. Rheological and bread-baking characteristics were related to results of the rapid tests. Highly significant cultivar differences were seen for all rheological and baking-related characteristics, and SRC and SIG parameters, with a strong genotype effect. The environment effect was also highly significant across regions, especially for flour protein content (FPC), which affected the rheological and baking-related characteristics differently across the regions. Correlations among SRC, SIG, rheological, and baking quality-related parameters were highly significant, but inconsistent for the two production regions. Only lactic acid SRC and SIG correlated consistently with the rheological and baking quality-related characteristics in both production regions.

Proline metabolism-related gene expression in four potato genotypes in response to drought stress

Drought severely limits potato yield. The aim of this work was to study a response of plantlets of four potato genotypes to polyethylene glycol (PEG 6000)-induced drought stress in both physiological and molecular levels. The drought-tolerant and drought-sensitive genotypes were identified based on plantlet growth, chlorophyll content, lipid peroxidation, free proline content, and proline metabolism-related gene expressions. We found that PEG-induced stress increased malondialdehyde (MDA) and proline content, and drought-tolerant plantlets exhibited lower MDA and proline content than sensitive genotypes. In addition, PEG up-regulated ∆-1-pyrroline-5-carboxylate synthase (P5CS) and pyrroline- 5-carboxylate reductase (P5CR) gene expressions and down-regulated pyrroline dehydrogenase (PDH) and ∆-1-pyrroline-5-carboxylate dehydrogenase (P5CDH) gene expressions. Genotype B plantlets exhibited lower P5CS and P5CR expressions and higher PDH and P5CDH expressions compared with the other plantlets. The results suggest that significant cultivar differences among potato plantlets in response to PEG-induced drought stress are exhibited in root length, MDA content, proline accumulation, and proline metabolism-related gene expressions.

The Phenolic Composition of South African Pinotage, Shiraz and Cabernet Sauvignon Wines

Phenolic compounds are major constituents of red wines and impact on certain wine-quality parameters. This study has aimed to increase the knowledge base on the phenolic composition of South African red wines by HPLC quantification of 39 individual phenols and 2 polymeric, phenolic groups in 260 South African wines of the cultivars Pinotage, Shiraz and Cabernet Sauvignon. Statistical analysis of the collected data revealed significant cultivar differences in the levels of many of the analysed compounds, as well as in the ratios in which specific anthocyanins are found in the wines. These data may be helpful in the cultivar authentication of wines of these cultivars. Discriminant analysis of the data showed statistically significant separations of cultivars, based on their polyphenol composition, and also how the use of data from a specific wine-producing area or vintage improved the possibilities for successful authentication. The data were collected from both pure cultivar wines and commercial wines, which may contain up to 15 % of another cultivar wine. The collected data may therefore be further segmented into those obtained from pure cultivar wines and those obtained from blended wines in order to further enhance the accuracy of authentication of these respective groups of wines. The information obtained from this study opens several avenues for research on the impact of the noted cultivar differences on wine quality. Cultivar differences in the phenolic composition of young red wines also have important implications for the oenological management of oxidation reactions taking place during vinification and aging.

Strawberry Cultivar Evaluation under High-tunnel and Organic Management in North Carolina

High-tunnel strawberry (Fragaria ×ananassa) production for extended seasons has a great economic potential for small farmers. However, information on cultivars that are suitable for high tunnels is rather limited. In this study conducted in the 2014–15 season, strawberry plugs of eight June-bearing cultivars (Florida Radiance, Benicia, Camarosa, Camino Real, Chandler, Strawberry Festival, Sweet Charlie, and Winterstar) and two day-neutral cultivars (San Andreas and Albion) were evaluated for yield performance, fruit quality, and vegetative growth in organically managed high tunnels at two locations in North Carolina. Significant cultivar differences in whole-season yield were observed at Greensboro, NC; but not at Goldsboro, NC. The cultivar Florida Radiance had the highest marketable and total yields, followed by Winterstar and Chandler at Greensboro, whereas Benicia, Winterstar, and Chandler were the top producing cultivars at Goldsboro. Harvest of day-neutral cultivars San Andreas and Albion started in November. For June-bearing cultivars, Florida Radiance began to produce harvestable berries in late December, followed by Winterstar in early January. Peak harvest occurred in April for all cultivars. At the end of the season, ‘Albion’ had smaller canopy size than other cultivars. It also developed the fewest number of branch crowns and least aboveground biomass. Total soluble solid (TSS) content in April was lower than that observed early and late in the season for all cultivars, although Strawberry Festival exhibited a relatively stable TSS throughout the season. ‘Benicia’ produced the largest strawberries in the early season, but its fruit weight was remarkably reduced as the season progressed. Severe frost events occurred on 18 and 20 Feb. that caused an average of 61.5% and 32.2% open blossom damage at Greensboro and Goldsboro, respectively. The recommended cultivars based on this 1-year study are Florida Radiance, Benicia, and Camino Real for June-bearing cultivars, and Albion and San Andreas for day-neutral cultivars.

Soil Water Tension Irrigation Criteria Affects Stevia rebaudiana Leaf Yield and Leaf Steviol Glycoside Composition

Stevia (Stevia rebaudiana Bertoni) is of interest for the production of steviol glycosides due to their noncaloric sweetening properties. Commercial stevia leaf production to date has focused on rebaudioside A and stevioside. Relatively little is known about the cultural practices necessary for the efficient production of stevia leaf and steviol glycosides. Irrigation management is an important agronomic technique that growers can use to obtain high yield while also pursuing water use efficiency (WUE). This trial investigated the effect that irrigation onset criteria measured as soil water tension (SWT) had on dry stevia leaf yields, steviol glycoside content and yield, and steviol glycoside ratios. Two stevia cultivars, SW 107 and SW 129 (S&W Seed Company Inc., Fresno, CA), were subjected to SWT irrigation criteria of 10, 20, 40, 60, and 80 kPa over a 57-day trial period at the Oregon State University (OSU) Malheur Experiment Station, Ontario, OR. Harvested plant material was evaluated for dry leaf yield and content of several steviol glycosides. Analysis of variance (ANOVA) showed significant cultivar differences in leaf yield, leaf stevioside and rebaudioside A content and yield, and steviol glycoside ratios (P = 0.05). Examining the data by ANOVA, dry leaf yield, stevioside percent, rebaudioside C percent, total steviol glycoside (TSG) percent, rebaudioside C yield, and TSG yield were significantly greater among the wetter (closer to 10 kPa) compared with the drier (closer to 80 kPa) SWT criteria treatments, yet a preferred treatment regime was not clearly evident. When comparing cultivars by regression analysis, there was a highly significant decrease in the stevioside content, and an increase in the ratio of rebaudioside A to stevioside from wetter to drier irrigation onset criteria (due to lower stevioside), whereas the rebaudioside A content did not respond significantly to differing irrigation criteria. Increasing dry leaf productivity with wetter irrigation criteria (closer to 10 kPa), directly increased the total rebaudioside A yield also, which in turn could provide increased crop value to the grower. Irrigating near 10 kPa produced higher dry leaf yield and total rebaudioside A yield, than irrigating at drier criteria.

Cultivar genetic gains from 50 years of irrigated sugarcane breeding in South Africa

Cultivar genetic gains provide a measure of benefits to growers from sugarcane breeding programmes and determine the effectiveness of cultivar development. The objective of this study was to determine the genetic gains for cane yield, percent estimated recoverable crystal (ERC%) cane and sugar yield of cultivars developed for the irrigated regions of South Africa after 50 years of sugarcane breeding. Data were derived from advanced cultivar trials planted in the early and mid-season in the Pongola and Mpumalanga regions. Significant (p < 0.01) cultivar differences were observed for cane and sugar yield and ERC% cane. There were significant (p < 0.05) season effects on ERC% cane and significant (p < 0.01) season by cultivar effects on ERC% cane and sugar yield, suggesting seasonal adaptation of cultivars. Cultivar genetic gains of 0.26 Mg ha−1 y−1 for cane yield, 0.03 Mg ha−1 y−1 for sugar yield and 0.06% y−1 for ERC% cane were observed. Genetic gains by sequence of release were 0.31 Mg ha−1 cultivar−1 for cane yield, 0.09 Mg ha−1 cultivar−1 for sugar yield and 0.06% cultivar−1 for ERC% cane. Cultivars released after 2000 produced genetic gains equivalent to 6% increase in sugar yield and 9% increase in ERC% cane compared with those released before 1990.

Assessment of Cultivar Distinctness in Alfalfa: A Comparison of Genotyping-by-Sequencing, Simple-Sequence Repeat Marker, and Morphophysiological Observations.

Cultivar registration agencies typically require morphophysiological trait-based distinctness of candidate cultivars. This requirement is difficult to achieve for cultivars of major perennial forages because of their genetic structure and ever-increasing number of registered material, leading to possible rejection of agronomically valuable cultivars. This study aimed to explore the value of molecular markers applied to replicated bulked plants (three bulks of 100 independent plants each per cultivar) to assess alfalfa ( L. subsp. ) cultivar distinctness. We compared genotyping-by-sequencing information based on 2902 polymorphic single-nucleotide polymorphism (SNP) markers (>30 reads per DNA sample) with morphophysiological information based on 11 traits and with simple-sequence repeat (SSR) marker information from 41 polymorphic markers for their ability to distinguish 11 alfalfa landraces representative of the germplasm from northern Italy. Three molecular criteria, one based on cultivar differences for individual SSR bands and two based on overall SNP marker variation assessed either by statistically significant cultivar differences on principal component axes or discriminant analysis, distinctly outperformed the morphophysiological criterion. Combining the morphophysiological criterion with either molecular marker method increased discrimination among cultivars, since morphophysiological diversity was unrelated to SSR marker-based diversity ( = 0.04) and poorly related to SNP marker-based diversity ( = 0.23, < 0.15). The criterion based on statistically significant SNP allele frequency differences was less discriminating than morphophysiological variation. Marker-based distinctness, which can be assessed at low cost and without interactions with testing conditions, could validly substitute for (or complement) morphophysiological distinctness in alfalfa cultivar registration schemes. It also has interest in sui generis registration systems aimed at marketing alfalfa landraces.

Yield and quality characteristics of day-neutral strawberry in the United States Upper Midwest using organic practices

The Upper Midwest of the US accounts for an extremely small portion of national strawberry (Fragaria x ananassa) production due to the prevalence of ‘June-bearing’ cultivars, which are limited to a short six-week fruiting window from June to early July. Determination of high yielding and high quality organically managed cultural practices for newer day-neutral cultivars in the region was performed. Six day-neutral cultivars were planted at two locations (St. Paul, and Morris, MN) in 2013 and 2014 and organically managed as annual crops under straw mulch, plastic mulch, and plastic mulch with low tunnel cultural practices. Yield and average berry weight for each cultivar/cultural practice combination was collected and analyzed weekly and cumulatively at each location and year. Total phenolic content (TPC) and total soluble solid (TSS) content of fruit was measured as indicators of nutritional and sensory quality over time. Day-neutral production added an average of fourteen weeks to the June-bearing strawberry season regardless of cultural practice, while all practices yielded more fruit than the 6160 kg ha–1 average for June-bearing production in the region. Significant cultivar differences within each practice were observed as well. TPC and TSS both displayed significant cultivar and time of harvest effects. Overall our data support the conclusion that day-neutral strawberries can perform well using organic cultural practices in the Upper Midwest, providing growers the opportunity to extend the season and bolster yield, while providing consumers access to nutritious, locally available fruit for a longer period of time.

Yield, Quality, and Storage Characteristics of Onion Cultivars in the Columbia Basin of Washington in 2012–14

An onion (Allium cepa) cultivar trial is conducted in the Columbia Basin of Washington every year. The trial helps onion growers, packers, processors, and seed companies compare cultivars and identify those most suited to their operations. This report evaluates 54 onion cultivars that were in the trials 2 years or more from 2012 to 2014. Marketable yields of cultivars averaged 764 to 1314 cwt/acre. ‘TTA-747’, ‘Scout’, ‘SV6672NW’, ‘Montero’, ‘XP07716000’, and ‘SV4058NV’ had the highest yields. All cultivars produced more jumbo-sized (3 to 4 inches) bulbs compared with any other size category, but those with the largest percentages of jumbo bulbs were Utrero, Gunnison, and Sedona. ‘Scorpion’, ‘Ruby Ring’, and ‘Purple Haze’ had the largest percentages of medium (2.25 to 3 inches) bulbs, and ‘Montero’ and ‘Ovation’ had the largest combined percentages of jumbo and colossal (&gt;4 inches) bulbs. Cultivar differences were evident in the 2012 and 2014 trials when many of the onions flowered (bolted). Cultivars averaged 0.0 to 15.5 bolted onions per plot when 2012 and 2014 results were combined. ‘Trekker’, ‘Highlander’, ‘Trailblazer’, ‘Ruby Ring’, ‘NUN8003ON’, and ‘Milestone’ had the fewest bolted onions. Cultivar differences were also apparent when several aspects of bulb quality were evaluated after 4 months in storage. ‘Utrero’, ‘Trekker’, ‘NUN7202ON’, and ‘Tamara’ had the most uniformly shaped bulbs. Bulbs of ‘Crockett’, ‘Legend’, and ‘Utrero’ had the most complete skins. ‘Crockett’, ‘Talon’, ‘Utrero’, ‘Legend’, ‘Gunnison’, and ‘Tamara’ had the firmest bulbs. Only 14 of 54 cultivars averaged more than 74% functionally single-centered bulbs. ‘NUN7202ON’, ‘Arcero’, ‘Joaquin’, and ‘Utrero’ had the largest percentages of bulbs with single centers or small multiple centers. There were more rots caused by bacteria (Enterobacter sp.) in bulbs produced in the 2014 trial than in 2012 and 2013, probably due to a high incidence of internal dry scale in 2014. Incidence of bacterial rot in cultivars was not significantly different in 2014, but there were some cultivar differences in 2012 and 2013. Incidence of fungal neck rot (caused by Botrytis sp.) in these trials was low and there were no significant cultivar differences. The results of these trials demonstrate that many new and advanced experimental cultivars have attributes that could make them a good choice for onion growers in the Columbia Basin.

BIOCHEMICAL CHANGES IN AMERICAN ELDER (SAMBUCUS CANADENSIS) FRUITS DURING DEVELOPMENT

For two consecutive years, total soluble solids, anthocyanins, free phenolics, and antioxidant capacity (ABTS/TEAC method) of the fruit of one wild ecotype and five cultivars of American elder (Sambucus Canadensis) were evaluated during development. All parameters increased significantly over the ripening period and reached a plateau at the purple stage. Significant yearly and cultivar differences were measured. Cultivars ‘Kent’ and ‘Nova’ showed significantly higher amounts of anthocyanins and phenolics along with a high antioxidant capacity. At maturity, anthocyanins, free phenolics, and antioxidant capacity were strongly correlated with each other (r2 = 0.82 to 0.97). The wild ecotype and all cultivars offer a high concentration in various compounds associated with a positive health effect and an antioxidant capacity higher than that of most cultivated small fruits from the same area of production. These compounds were more abundant in cultivars ‘Scotia’ and ‘York’ when grown in L’Acadie (Quebec) than in Corvallis (Oregon). Optimal elderberry quality can be obtained by selecting appropriate harvest date. Periodic determination of total soluble solids content could be used to support visual observation, given that it tends to stabilize when the berries reach full maturity. Our results indicate that there are significant differences in phytochemical profiles and antioxidant activity among the tested cultivars. Selection should be based on adequate chemical characterization in parallel with field performance.

A Simple Method for the Assessment of Fusarium Head Blight Resistance in Korean Wheat Seedlings Inoculated with Fusarium graminearum.

Fusarium head blight (FHB; scab) caused mainly by Fusarium graminearum is a devastating disease of wheat and barley around the world. FHB causes yield reductions and contamination of grain with trichothecene mycotoxins such as deoxynivalenol (DON) which are a major health concern for humans and animals. The objective of this research was to develop an easy seed or seedling inoculation assay, and to compare these assays with whole plant resistance of twenty-nine Korean winter wheat cultivars to FHB. The clip-dipping assay consists of cutting off the coleoptiles apex, dipping the coleoptiles apex in conidial suspension, covering in plastic bag for 3 days, and measuring the lengths of lesions 7 days after inoculation. There were significant cultivar differences after inoculation with F. graminearum in seedling relative to the controls. Correlation coefficients between the lesion lengths of clip-dipping inoculation and FHB Type II resistance from adult plants were significant (r=0.45; P<0.05). Results from two other seedling inoculation methods, spraying and pin-point inoculation, were not correlated with adult FHB resistance. Single linear correlation was not significant between seed germination assays (soaking and soak-dry) and FHB resistance (Type I and Type II), respectively. These results showed that clip-dipping inoculation method using F. graminearum may offer a real possibility of simple, rapid, and reliable for the early screening of FHB resistance in wheat.

Selection for Resistance to the Rhizoctonia-Bacterial Root Rot Complex in Sugar Beet.

The Rhizoctonia-bacterial root rot complex continues to be a concerning problem in sugar beet production areas. To investigate resistance to this complex in 26 commercial sugar beet cultivars, field studies and greenhouse studies with mature roots from the field were conducted with Rhizoctonia solani anastomosis group 2-2 IIIB strains and Leuconostoc mesenteroides. Based on means for the 26 cultivars in the 2010 and 2011 field studies, fungal rot ranged from 0 to 8%, bacterial rot ranged from 0 to 37%, total internal rot ranged from 0 to 44%, and surface rot ranged from 0 to 52%. All four rot variables resulted in significant (P < 0.0001) cultivar differences. Based on regression analysis, strong positive relationships (r2 from 0.6628 to 0.9320; P < 0.0001) were present among the rot variables. When ranking cultivars, the most consistent rot variable was surface rot, because 12 of 13 variable-year combinations had significant (P ≤ 0.05) correlations. When cultivar ranking in greenhouse assays was compared, there was frequently a positive correlation with storage data but no relationship with field results. Thus, the greenhouse assays will identify storage rot resistance but field screening will be required to find resistance to this rot complex in the field.

Effect of temperature on the life cycle of Heterodera schachtii infecting oilseed rape (Brassica napus L.)

Oilseed rape (OSR; Brassica napus L.) is a crop of increasing world importance and suffers yield loss when infected with Heterodera schachtii. The in vitro hatch, in planta root invasion and development of a field population of H. schachtii were investigated in six thermostatically-controlled water baths at temperatures of 5.0, 10.1, 20.5, 27.8, 32.2 and 37.5°C in a glasshouse. The UK winter OSR cvs Flash and Castille were used. Temperature was shown to have a major influence on the development of H. schachtii in OSR. The highest cumulative percentage hatch of second-stage juveniles (J2) observed over an 8-week incubation period occurred between 20.5 and 27.8°C in leachates of both OSR cultivars, indicating that this is the optimum temperature range for hatching of this population. Cumulative hatch was lowest at 37.5 and 5.0°C. Root invasion was inhibited at 5.0 and 37.5°C, whilst the highest number of J2 invaded the roots between 20.5 and 32.2°C, indicating that this is the optimum temperature range for root invasion. The life cycle took between 21 days at 20.5°C and 42 days at 5.0°C from the inoculated J2 to the J2 of the second generation, with the associated accumulated heat units (AHU) of 424 and 203 degree-days with a base temperature (Tb) of 5.0°C. The optimum temperature range (To) for development was between 20.5 and 27.8°C and the maximum (Tm) was 37.5°C. As temperature increased, the AHU required to complete the life cycle increased from 203 degree-days at 5.0°C to 1406 at 37.5°C. Leachates from both OSR cultivars stimulated more J2 to hatch than the distilled water controls. No significant cultivar differences were observed for J2 hatching, root invasion and duration of the life cycle at the different temperatures but significantly more cysts of the second generation (g root)−1 were observed in cv. Flash than cv. Castille at 27.8 and 32.2°C, suggesting that the latter cultivar is a poorer host of H. schachtii than cv. Flash. This is the first report of the effect of temperature on H. schachtii development on current winter OSR cultivars in the UK and provides insight into the potential effects of climate change on the nematode-host interaction.

Mineral Concentration of Broccoli Florets in Relation to Year of Cultivar Release

ABSTRACTIt has been proposed that crop improvement through directed plant breeding has resulted in decreases in nutrient concentrations of harvested components over time. A few field studies wherein cultivars released over a period of years are evaluated for nutrient content provide the best evidence for nutrient changes over time; however, no such studies have been conducted with vegetable crops. To accomplish this with broccoli (Brassica oleracea L.), we grew 14 cultivars released over 50 yr in two field trials, and harvested florets were assayed for mineral concentration by inductively coupled plasma–optical emission spectroscopy. Results indicated significant cultivar differences in floret concentrations of Ca, Cu, Fe, Mg, Na, P, and Zn, but not of K, Mn, Mo, or S. With most minerals, there was no clear relationship between concentration and release year. Although the oldest cultivar exhibited some of the higher mineral concentrations, from 1975 to the present no significant changes appear to have occurred. Head mass was negatively correlated with concentrations of most minerals, but head mass was not correlated with year of release. We propose it most relevant to examine mineral nutrient changes for cultivars grown since 1975 when broccoli phenotypes changed dramatically and the vegetable grew in prominence as a component in the U.S. diet. Results provide a guide for mineral levels in broccoli that should be maintained as other characteristics are manipulated in the future.

Relative Infestation and Damage of Some Pigeonpea Cultivars by Lepidopteran Pod Borers in Uganda

Infestation and damage of some pigeonpea ( Cajanus cajan [L.] Millsp.) cultivars by lepidopteran pod borers were evaluated over two cropping seasons during 1991 at the Makerere University Agricultural Research Institute, Kabanyolo. Significant (P&le;0.05) cultivar differences were recorded in borer incidence and pod damage. Apio, the local cultivar, showed the highest infestation by Helicoverpa armigera (Hubner). ICPL 87104 had the greatest infestation by Maruca testlalis (Geyer), although in the second season it was not significantly higher than the rest. Etiella zinckenella (Treitschke) occurred in very low numbers, and cultivar differences were not significant (P &gt; 0.05). Indexing larval counts to number of pods per plant showed that infestation pressure by both H. armigera and M. testulalis was not as different among cultivars as larval counts suggested. Pod damage was greatest on ICPL 87 and lowest on ICPL 87104.Keywords: Pigeonpea, pod borers, Uganda

Physiological and morphological diversity of cultivated strawberry ( Fragaria × ananassa) in response to water deficit

A first step in breeding for improved water use efficiency is to determine the extent of adaptation to limited water availability already existing between cultivars. Cultivation of strawberry ( Fragaria × ananassa Duch.) requires irrigation, but to date drought tolerance of different cultivars has not been explored; indeed there has been only limited research on between-cultivar variation for drought tolerance in any fruit crop. To address this issue, 10 cultivars were compared when irrigated to match 100% (control), or less than 70% (water deficit), of evapotranspiration. Transpiration rate, numbers and area of new leaves, dry mass of leaves and roots, and leaf water potential were significantly reduced under the water deficit treatment. Root to shoot dry mass ratio was significantly increased. Water use efficiency (WUE), measured as marketable yield per litre water transpired, increased under water deficit. There were significant cultivar differences for all these variables, and also for photosynthetic rate and for transpiration efficiency (TE), measured as biomass per litre water transpired. Of the two cultivars traditionally grown without irrigation (rain-fed only), one (‘Cambridge Favourite’) showed very high transpiration rates, while the other (‘Totem’) showed very low transpiration rates. Transpiration rates were low for ‘Elvira’, which has been previously considered as drought susceptible, but this was also true of ‘Idea’, which has been considered drought tolerant. Total transpiration was significantly correlated with final leaf area and total biomass. WUE of ‘Elvira’ was high but TE was low. On the other hand, WUE of ‘Hapil’ (for which there is anecdotal evidence of drought tolerance) and ‘Totem’ was low and TE high. ‘Idea’ showed intermediate WUE and TE. Since variation between cultivars in plant canopy and growth and transpiration efficiency was not strongly influenced by environment, genotypic variation in these variables could be utilised in a breeding programme for improved drought tolerance in strawberry. On the other hand, a significant interaction of cultivar and irrigation was found for stomatal conductance, midday osmotic potential at full turgor, marketable yield, and berry mass, suggesting that mechanisms of response to water deficits are not uniform across cultivars.

Cultivar differences in the deterioration of vase-life in cut-flowers of Anthurium andraeanum is determined by mechanisms that regulate water uptake

Vase-life, average daily water uptake rate and abaxial stomata density were evaluated in 17 anthurium ( Anthurium andraeanum Hort.) cultivars over two trials. There were significant cultivar differences for vase-life (14–49 days), 5-day average water uptake rate and abaxial stomata density, in both trials. A progressively stronger correlation coefficient between average daily water uptake rates during the period 25–50 days after initiation of experiment (DAI) and vase-life was observed, indicating that cultivars with longer vase-life were able to maintain above average water uptake rate over a longer period of time and hence delay symptoms of water stress. This was evident in the water uptake rate curves as an inflection, resulting in the levelling off of water uptake rates. The cultivars with long vase-lives achieved steady state water uptake levels faster, and maintained a high steady state water uptake rate for longer durations. The role of vascular occlusion and other senescence factors on water relations and vase-life is discussed.

Relative Susceptibility of Selected Apple Cultivars to Apple Scab Caused by Venturia inaequalis

Apple scab is the most important disease of apples (Malus domestica) in the cool temperate regions where apples are grown. Data were collected over several years from plantings of new apple cultivars and selections established at multiple locations in 1995 (23 entries) and 1999 (24 entries) as part of regional project NE-183. Golden Delicious and McIntosh were the standards in both plantings. Data on incidence of scab on leaves and fruit were collected and analyzed to determine differences due to location and cultivar. None of the analyses indicated significant cultivar differences due to location, likely confirming the diversity of the apple scab fungus in the eastern United States. In general, for scab on leaves, the cultivars Ginger Gold, Orin, Cripps Pink, Silken, and Delblush were as susceptible as McIntosh, a common standard for scab susceptibility in the eastern United States. For scab on fruit, the cultivars Fuji, Cameo, Cripps Pink, Ambrosia, and Silken, and the selection NJ 90, were as susceptible as McIntosh. As expected, the cultivars and selections with genetic resistance to the scab pathogen exhibited the lowest incidences of apple scab on foliage and fruit. Gala Supreme, Sansa, and Honeycrisp, while susceptible to scab, exhibited relatively low levels of the disease. Accepted for publication 2 February 2010. Published 8 April 2010.