Varietal differences in the response of potatoes to repeated short periods of water stress in hot climates. 2. Tuber yield and dry matter accumulation and other tuber properties

Summary The effect of repeated short periods of water stress during the hot season on six potato cultivars was investigated. The number of tubers per plant tended to decrease in response to water stress in cultivars which had more than 9.8 tubers per control plant (Désirée, Alpha, Elvira). In the other cultivars, no consistent effect of water stress on tuber number per plant was observed. Except for Spunta, the percentage of large tubers (>60 g/tuber) was reduced in the water-stressed plants. Consequently, the average weight of these tubers was greater than that of tubers harvested from the unstressed plants, indicating that the sink force of the individual tuber was not impaired by drought. However, tuber yield per plant was reduced due to drought in all cultivars tested. The smallest decrease in dry matter accumulation as well as the greatest lowering of the osmotic potential in the tuber tissue was found in Alpha. No consistent effect of water stress on the percentage of misshapen and sprouting tubers was observed, indicating the marked effect of the high temperature on these traits. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No 310-E, 1981 series. This investigation was sponsored by a grant from the Ministry for Development Cooperation of the Netherlands.     

Reduction of leaf growth by water stress and its recovery in relation to transpiration and stomatal conductance in some potato (Solanum tuberosum L.) genotypes

Summary The effect of water stress (5 days of no watering) on leaf growth and its subsequent recovery after 5 days of watering was investigated in potted plants of eight potato (Solanum tuberosum L.) genotypes. The genotypes fell into three groups. Group A was characterized by minimum growth reduction under stress and rapid recovery on rewatering with final increase in leaf length exceeding that of the unstressed controls. In Group B, stress created moderate reduction in growth and on recovery the increase in leaf length became comparable to that of controls. Group C was characterized by large growth reduction and rewatering did not result in final leaf length increases comparable to that of controls. Statistical analysis showed a negative correlation between reduction in growth and stomatal conductance (r=−0.917;P<0.01) and between reduction in growth and transpiration (r=−0.912;P<0.01). CPRI Publication No. 812.     

Responses of cassava (Manihot esculenta Crantz) cultivars to in vitro-induced phosphorus stress

Rapid identification of phosphorus (P) stress-tolerant cassava varieties by in vitro and molecular screening is essential for sustainable food production. The objectives of this study were to describe morphological and molecular responses of 10 cassava cultivars to in vitro-induced P stress and identify P-stress-tolerant ones. Plantlets were raised from nodal segments on Murashige and Skoog (MS) medium containing either P or no P (control). The ?tudу was conducted as a 2 × 10 factorial arrangement using a randomized complete-block design with thrее rерliсаtе?. On P-stress medium, TMS 01/1371 did not produce roots, TMS 94/0039 produced roots after three weeks, and MM 96/1751, MM 98/3437, TMS 01/0040, TMS 30040, TMS 84/00353, TMS 91934, TMS 92B/00061, and TMS 94/0026 produced roots after six weeks. Phosphorus-stress treatment reduced number of leaves, number of roots, and number of shoots by 41.8%, 214.7%, 139.2%, respectively. Similarly, P-stress treatment decreased dry weight (DW) of TMS 01/0040, TMS 01/1371, TMS 84/00353, TMS 91934, TMS 92B/00061, and TMS94/0026 by an average of 10.2%. However, P-stress treatment increased DW of MM 96/1751, MM 98/3437 and TMS 94/0039 by an average of 8.4%; P-stress treatment had no effect on DW of TMS 30040. Expression of MeWRKY gene was higher in roots than in leaves of all cultivars by an average of 88.1%. Stress tolerance index relative to P showed that MM 96/1751, MM 98/3437, TMS 94/0039, and TMS 30040 were P-stress tolerant and therefore recommended for breeding and for production to farmers.     

Root growth,soil water variation,and grain yield response of winter wheat to supplemental irrigation

Water shortage threatens agricultural sustainability in the Huang-Huai-Hai Plain of China. Thus, we investigated the effect of supplemental irrigation (SI) on the root growth, soil water variation, and grain yield of winter wheat in this region by measuring the moisture content in different soil layers. Prior to SI, the soil water content (SWC) at given soil depths was monitored to calculate amount of irritation water that can rehydrate the soil to target SWC. The SWC before SI was monitored to depths of 20, 40, and 60 cm in treatments of W20, W40, and W60, respectively. Rainfed treatment with no irrigation as the control (W0). The mean root weight density (RWD), triphenyl tetrazolium chloride reduction activity (TTC reduction activity), soluble protein (SP) concentrations as well as catalase (CAT), and superoxide dismutase (SOD) activities in W40 and W60 treatments were significantly higher than those in W20. The RWD in 60–100 cm soil layers and the root activity, SP concentrations, CAT and SOD activities in 40–60 cm soil layers in W40 treatment were significantly higher than those in W20 and W60. W40 treatment is characterized by higher SWC in the upper soil layers but lower SWC in the 60–100-cm soil layers during grain filling. The soil water consumption (SWU) in the 60–100 cm soil layers from anthesis after SI to maturity was the highest in W40. The grain yield, water use efficiency (WUE), and irrigation water productivity were the highest in W40, with corresponding mean values of 9169 kg ha^?1, 20.8 kg ha^?1 mm^?1, and 35.5 kg ha^?1 mm^?1. The RWD, root activities, SP concentrations, CAT and SOD activities, and SWU were strongly positively correlated with grain yield and WUE. Therefore, the optimum soil layer for SI of winter wheat after jointing is 0–40 cm.     

The response of potatoes to a single transient heat or drought stress imposed at different stages of tuber growth

Summary The effects of a single treatment of heat or drought stress imposed at different stages of tuber growth, were investigated in two potato cultivars, Désirée and Cara. Both stresses impaired dry matter accumulation in tubers, and tuber yields. Stress imposed at early stages of tuber growth, when tubers were less than 20 mm in diameter, had little effect on dry matter accumulation, whereas stress imposed later resulted ingnificant losses of dry matter in tubers. Stress imposed during later tuber growth increased the percentage of tubers sprouting in the soil. Tuber malformation was less affected. The adverse effects of heat on tuber yield and quality seemed to be greater than those of drought. Drought increased the content of total soluble solids (TSS) and lowered the osmotic potential in the tuber tissue of both cultivars. These effects were detectable even 55 days after stress relief. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel No 984-E, 1984 Series. This investigation was sponsored by a grant from the Ministry of Foreign Affairs, Technical Assistance Department, Netherlands.     

Evaluation of treatments with hot water,chemicals and ventilated containers to reduce microbial spoilage in irradiated potatoes

Summary Potatoes irradiated to control sprouting were dipped in: hot water (56°C, 5 min; 52°C, 10, 15 and 20 min); cold (25°C, 5 min) or hot (56°C, 5 min) salicylic acid (1000 and 2000 ppm); or sodium hypochlorite (0.1 and 0.2%, 5 min); or dusted with salicylic acid (1 and 2%), to try to reduce the incidence of bacterial soft rot (Erwinia sp.) during controlled temperature (10°C, 15°C) and ambient temperature (20–34°C) storage. All treatments, particularly hot water and hot salicylic acid dip, increased microbial spoilage, possibly as a result of handling damage during the treatments combined with the inhibition of wound periderm formation as a result of irradiation. Storing irradiated tubers in well ventilated containers reduced soft rot compared to storing them in sacks and after 6 months storage at 10, 15 and 20–34°C, 95, 90 and 77% respectively were healthy and marketable.     

Yield response of potato genotypes to different soil water regimes in contrasting seasons of a subtropical climate

Summary Potato crops in subtropical climates are often subjected to water stress, resulting in low yields and poor tuber quality. The yield response of potato genotypes to water supply was investigated in six trials, three each in spring and autumn plantings. Trials were conducted under automated rain shelters, using an irrigation boom to impose five soil water regimes. The negative effect of water stress on tuber yield was more detrimental in spring than in autumn, because of higher atmospheric evaporative demand and higher temperatures in spring. An average yield reduction of 68% was recorded for the most severely stressed regime in spring plantings, while the mean reduction for the same treatment in autumn was only 42%. Genotypic differences in yield response to drought were clearly illustrated in spring, but not in autumn. This suggests that the choice of genotypes is only influenced by the availability of water in spring, when more drought tolerant genotypes should be used.     

Germination responses of the halophyte Chloris virgata to temperature and reduced water potential caused by salinity,alkalinity and drought stress

Chloris virgata is considered a useful grass species for grassland restoration in northern China. However, little information exists concerning the germination responses of this species to temperature and water potential caused by stress conditions. Experiments were conducted in growth chambers to assess the effect of temperature, salinity, alkalinity, drought and the interactions of temperature and stress on seed germination. Seeds were germinated at three diurnal temperature regimes, with four water potentials in NaCl, NaHCO₃ and PEG solutions. Results showed that optimal germination under stress occurred at 15–25 °C, and germination percentages and rates were inhibited by either an increase or decrease in temperature from the optimal temperature. The inhibitory effects of the low water potential caused by salinity and drought on germination were greater at 25–35 °C, but seeds were subjected to more stress despite the relatively higher water potential because of the alkalinity at this temperature. The recovery percentage under salinity was highest at ?1·2 MPa at 15–25 °C, and more than 80% of seeds also germinated at this water potential after they were transferred from drought stress. However, seeds lost their viability in higher alkalinities under all temperatures, and at 25–35 °C, there was lower recovery percentage under stress. Results suggest that salinity, alkalinity and drought stress have different impacts on seed germination, and the tolerance to stress of C. virgata seeds is affected by the interactions of temperature and water potential caused by salinity, alkalinity and drought. Chloris virgata shows potential utility as a promising grass species in salinity–alkalinity and drought‐stressed environments.     

Genotypic variation in the response of potatoes (Solanum tuberosum L.) to high ambient temperatures and water deficit

The response of potatoes to the major environmental stresses which prevail in a hot-dry climate, i.e., high temperature and water deficit, was studied. Nine potato cultivars and one unnamed clone of contrasting maturity classification were tested in the field under favorable climatological conditions in the spring and under high temperature conditions in the summer. In both seasons the plants were subjected to moderate and severe water deficits. In the spring, yield losses of 0 – 44% and 0 – 47% of fresh and dry weights, respectively, were obtained under moderate water stress, and losses of 16 – 55% and 2 – 52% of fresh and dry weights, respectively, under severe water stress. Under high ambient temperatures in the summer season and with adequate water supply, yield losses ranged from 0 – 96% compared with the spring crop yields, indicating the extreme susceptibility of some genotypes to heat stress. In all cultivars yield losses due to drought were much greater in the summer than in the spring. The early cultivars ‘Blanka’ and ‘Monalisa’ were less sensitive to changes in the environment, while the later maturing cultivars ‘Cara’ and ‘Desiree’ were very sensitive, being the highest yielding cultivars under the most favorable conditions. Early maturation was closely correlated with smaller yield losses in the summer, pointing to the possible involvement of an escape mechanism in the tolerance to heat stress. The differential response of the various genotypes to drought indicates the possible improvement of tolerance to drought in the potato. The possibility of improving adaptation to high temperatures is discussed.     

结荚鼓粒期土壤水分胁迫对不同大豆品种形态和生理特性的影响

为探讨土壤水分胁迫对大豆品种形态性状和生理特性的影响,以3个抗旱性不同的大豆品种(合丰25、黑农44、晋豆21)为试验材料,在盆栽条件下,于大豆始荚期至鼓粒期进行中度和严重土壤水分胁迫试验,对形态性状、叶绿素含量、光合速率、超氧化物歧化酶(SOD)活性、过氧化物酶(POD)活性、过氧化氢酶(CAT)活性进行测定.结果表...     

水稻理想株形育种的理论和方法再论——叶片质量的品种间差异及其与产量因素的关系

水稻理想株形育种确是高光效育种,因而应以遗传及生理两方面的知识作为理论基础。反映叶片质量的比叶重和叶绿素含量,品种间差异很大,但前者又比后者受环境的影响较小。除比叶重和叶绿素含量之间有明显的正的关系外,两者都与叶片含氮量有极显著正相关,后者又与净同化率有极显著的正相关。叶面积、比叶重和叶绿素含量与每穗成粒数、平均穗重都有极显著的正相关,其大小顺序为叶面积＞比叶重＞叶绿素含量。在后二者中,比叶重对穗重的直接贡献较大,叶绿素含量对干物重的作用则越到后期越明显。因此水稻理想株形的高光效育种在重视叶面积的同时,还应注意比叶重和叶绿素含量。上述叶片三个性状的测定方法都比测含氮量简便,且都可用目测（叶面积和叶绿素含量）或手感（比叶重高者其叶厚挺）,这对田间筛选大量材料具有实用意义。     

干旱胁迫及复水下朱槿生长及根际土壤微生物多样性的变化特征

以朱槿品种‘紫牡丹’为试验材料,采用盆栽试验,研究了苗期重度干旱胁迫及复水对其根系生理特性的影响,并运用高通量测序技术分析干旱胁迫及复水下朱槿根际土壤微生物多样性的变化特征。结果显示：与正常处理（CK）相比,重度干旱胁迫及复水处理（T2）的总根长、根表面积及根尖数等根系生长指标呈现显著减少的结果,但与重度干旱胁迫（T1）处理相比,均显著增加。通过对朱槿根际土壤样品中细菌群落结构的研究发现,属分类水平上,厌氧绳菌属（Anaerolineaceae）,酸杆菌属（Acidobacteria）、酸微菌属（Acidimicrobiales）、幽门螺杆菌属（Sphaerobacter）、链霉菌属（Streptomyces）等是不同处理土壤样品中的优势菌群。T1处理下的嗜青霉属（Algiphilus）、奥利螺旋菌属（Aureispira）、绿线菌属（Chloronema）、扁棒壳属（Acrospermum）为不同处理下的特殊细菌。真菌方面,属的分类水平上发现,粪壳菌属（Sordariale）、散囊菌属（Eurotiales）、拟青霉属（Pseudallescheria）、格孢腔菌属（Pleosporales）、枝孢霉属（Cladosporium）等是不同处理土壤样品中的优势菌群;T1和T2处理下的样品中,侧角藻属（Goniomonas）、齿盘菌属（Lamprospora）和索罗迪夫斯菌属（Sorodiplophrys）为不同处理下的特殊真菌属。其中,有促生作用的细菌如酸微菌属( Acidimicrobium)、厌氧绳菌属（Anaerolineaceae）嗜青霉属（Algiphilus）以及具有一定生防作用真菌如拟青霉属（Pseudallescheria）、枝孢霉属（Cladosporium）等均可以合理的应用在农业生产中,为植物的抗干旱胁迫以及提高朱槿在干旱胁迫下的水分利用做出贡献。     

Root development and the expression of aquaporin genes in rice seedlings under osmotic stress

We conducted hydroponic culture experiments to characterize root traits in a rice cultivar ‘Puluik Arang’ that has been identified in a previous study as a cultivar that is adaptable to unflooded conditions. Root morphological traits and the expression of 11 aquaporin genes in rice seedlings (cv. Puluik Arang and cv. Akitakomachi) subjected to osmotic stress by polyethylene glycol (PEG) treatments (10 and 20%) were analysed. ‘Puluik Arang’ exhibited significantly greater water uptake under 10% PEG treatment than ‘Akitakomachi’. Lateral root development was maintained in ‘Puluik Arang’ under PEG treatments. The expression of some aquaporin genes, particularly OsTIP2;1, was higher in ‘Puluik Arang’ than in ‘Akitakomachi’. Immunocytochemical analysis showed that the OsTIP2;1 protein mainly accumulated in endodermal cells. The results suggest that better lateral root development and the function of aquaporins could contribute to water uptake in ‘Puluik Arang’ under osmotic stress.     

Growth and yield studies of potatoes developed in a semi-arid region 1. Yield response of several varieties grown as a double crop

Summary The yielding capacity of European potato varieties was tested in the spring and the autumn. The environmental characteristics for the spring crop (February–June) are increasing day length and temperature from planting to harvest, with the opposite for the autumn crops (August–December). In the spring crop, using imported seed tubers of about 5–6 months' chronological age, the stem density of different varieties varied between 120 000 and 240 000 per ha, and the weekly yield rates (total yield/growth period) were 2.6 and 4.7 t/ha. In the autumn crop, when local seed tubers of 3 months' chronological age were planted, the stem density was 2–3 times lower and the weekly yield rates were between 1.6 and 3.9 t/ha. Two groups of potato varieties were selected according to their yield performance as being suitable: a) for the spring crop cvs. Up-to-Date, Désirée and ZPC 71E207; and b) suitable for the autumn crop cvs. Désirée, Draga, Gulliver, Spunta, Ropta A3802, ZPC 71E277, and Cardinal. The variability in yield response of theS. tuberosum varieties to the high temperatures and short photoperiods of the semi-arid environment is discussed. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 280-E, 1980 series.     

Simulating water use and N response of winter wheat in the irrigated floodplains of Northwest Uzbekistan

The crop-soil simulation model CropSyst was used to simulate growth, water- and N-uptakes of irrigated winter wheat (Triticum aestivum L. cv. Kupava) in Khorezm, in the dry lands of northwest Uzbekistan, Central Asia. CropSyst was calibrated using the findings of field experiments of 2005/06 and 2006/07 and validated for the 2007/08 season. A relative root mean squared error of 11% proved the accuracy between simulated and observed aboveground biomass and grain yield in 2007/08. Scenario analyses showed that N-leaching was high and ranged from 63 to 106 kg ha⁻¹ when irrigated between 749 and 869 mm during the first two cropping seasons. The simulated N-leaching was lowest and ranged from 7 to 15 kg ha⁻¹ when irrigation was only 148–395 mm during 2007/08. The considerable N losses during leaching and high N-uptakes by wheat together resulted in a negative N-balance even during applications of 180 and 240 kg ha⁻¹ of N-fertilizer. N scarcity in the N-balance was reduced with increasing N-fertilizer amounts and ranged from −29 to −153 kg N ha⁻¹ in 2005/06 and 2006/07. Despite a common shallow groundwater table in the region during some time of the year, scenario analysis revealed that only full irrigation water (580 mm) and N supply according to crop demand (180 kg ha⁻¹) guaranteed high grain yields, unless the water table is permanently shallow to overcome irrigation deficits. Limited irrigation and N application (40% and 55% of ‘optimal’, respectively) in combination with a groundwater table below 3 m resulted in a 55% yield decline. The CropSyst wheat model proved a robust tool for assessing the influence of water and N dynamics under conditions of varying irrigation and shallow groundwater tables. It thus has potential as a decision support not only in northwest Uzbekistan, but also in comparable regions of Central Asia.     

Crop water use indicators to quantify the flexible phenology of quinoa (Chenopodium quinoa Willd.) in response to drought stress

Models can play an important role in agricultural planning and management. Thermal time accumulation is a common way of describing phenological development in crop models, but the sensitivity of this concept to water stress is rarely quantified. The effect of pre-anthesis droughts on the timing of anthesis and physiological maturity was assessed for quinoa (Chenopodium quinoa Willd.) var. ‘Santa Maria’, with the help of two field experiments (2005–2006 and 2006–2007) in the central Bolivian Altiplano. Various treatments with different sowing dates and irrigation applications were considered. To evaluate the effect of drought stress on crop development, drought stress during the first 60 days after sowing was assessed with three different stress indicators: the number of days that the soil water content of the root zone was above a threshold, the average relative transpiration, and the sum of daily actual transpiration, standardized for reference evapotranspiration (∑(T_a/ET₀)). The best indicator to quantify the effect of pre-anthesis drought stress on phenological development was ∑(T_a/ET₀) cumulated until 60 days after sowing. This indicator showed a significant logarithmic relation with the time to anthesis and time to physiological maturity. Correlations of the drought stress indicator with thermal time accumulation were better than with calendar time accumulation. Due to an effect of post-anthesis droughts, the correlations of the drought stress indicator with the time to anthesis were stronger than with the time to physiological maturity. It was also demonstrated that deficit irrigation can contribute to a better agricultural planning due to a better control of the phenological development of quinoa. The proposed relations can be used for modeling phenological development of quinoa in drought prone regions and for efficient deficit irrigation planning.     

Genotypic variation in patterns of root distribution, nitrate interception and response to moisture stress of a perennial ryegrass (Lolium perenne L.) mapping population

Genotypic variation in patterns of root distribution, nitrate interception and response to moisture stress were assessed in both parents and 198 progeny of a perennial ryegrass (Lolium perenne L.) full‐sibling mapping population. This was carried out in metre‐deep tubes of sand culture in a glasshouse experiment. The proportion of root dry matter (DM) weight in the top 10 cm of sand ranged from 0·33 to 0·75 and values of log₁₀(1 ? K), where K is the constant for an exponential model relating root DM weight and root depth, also showed wide variation among genotypes. The proportion of a pulse of ¹⁵N recovered in whole plants ranged from 0·124 to 0·431. There was a positive linear correlation between the proportion of ¹⁵N recovered and plant total DM weight, but no relationship between nitrate interception and patterns of distribution of DM weight of roots. Some genotypes responded to moisture stress by increasing root growth, and in others root growth was inhibited. It is concluded that this below‐ground variability in root variables may be an evolutionary adaptation by plant populations to survive heterogeneity in soil biotic and edaphic factors.     

Nitrate in potatoes. 1. The effect of fertilization and storage on the nitrate content in 5 genotypes grown in widely separated localities

Summary The effect of nitrogen fertilizer at levels of 50, 100 and 150 kg per ha, and of the length of storage on the nitrate content of potatoes was studied in field experiments. Five genotypes were grown at five sites differing widely in day length, temperature and precipitation. The nitrate concentration of the tubers increased significantly with increasing nitrogen supply, but less in some genotypes than in others and there were significant differences between localities. The highest nitrate concentration was found at the locality with the coolest growing season, the lowest at one with a relatively high summer temperature. Nitrate in tubers decreased significantly during storage periods of 90 and 180 days. The overall concentration of nitrate in the tubers was low event at the highest N dressing, and the tubers can safely be recommended for human consumption.

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Zusammenfassung Der Einfluss von Stickstoffdüngung (50, 100 und 150 kg/ha) und Lagerungsdauer auf die Nitratkonzentration in Kartoffeln wurde im Feldversuch untersucht. Fünf Genotypen wurden in 5 ausgew?hlten Gebieten angebaut, die im Hinblick auf Tagesl?nge, Temperatur und Niederschl?ge grosse Unterschiede aufwiesen. Mit steigender Stickstoffzufuhr wurde eine signifikante Erh?hung der Nitratkonzentration nachgewiesen, wobei sowohl zwischen den verschiedenen Genotypen (Tab. 1) als auch Anbaugebieten (Tab. 3) die Unterschiede gesichert waren. Die h?chste Nitratkonzentration wurde in Kartoffeln nachgewiesen die im k?ltesten Anbaugebiet geerntet wurden, die geringste Nitratkonzentration in Kartoffeln aus Anbaugebieten mit verh?ltnism?ssig hoher Sommertemperatur. Die Nitratkonzentration der Knollen verringerte sich w?hrend der Lagerungsdauer von 90–180 Tagen signifikant (Tab. 2). Durchschnittlich wurden selbst bei der h?chsten Stickstoffdüngung verh?ltnism?ssig niedrige Nitratkonzentrationen in den Kartoffelknollen gemessen. Daher bestehen gegen die Verwendung der Kartoffeln für den menschlichen Verzehr keine gesundheitlichen Bedenken.

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Résumé L'influence de la fertilisation azotée (50, 100 et 150 kg/ha) et de la durée de conservation sur la teneur en nitrate dans les pommes de terre a été étudiée en expérimentations de plein champ. Cinq génotypes de pommes de terre ont été cultivés dans cinq localités qui diffèrent, entre elles, par la longueur de jour, la température et l'humidité. La teneur en nitrate dans les tubercules augmente de fa?on significative avec l'apport d'azote, mais en moindre proportion pour certains génotypes (tabl. 1). La différence entre les localités est également significative (tabl. 3). La plus forte teneur est observée dans la localité ayant la période de végétation la plus froide, tandis que la plus faible teneur correspond à une température estivale relativement élevéc. La teneur en nitrate dans les tubercules diminue de fa?on significative pendant les périodes de conservation de 90 à 180 jours (tabl. 2). La teneur moyenne en nitrate demeure faible dans les tubercules, même pour la fertilisation la plus élevée. C'est pourquoi, les tubercules ne présentent aucun risque pour la consommation humaine.

     

Responses of SUB1 rice introgression lines to submergence in the field: Yield and grain quality

Prolonged submergence is a major constraint to rice production, affecting over 15 million ha in South and Southeast Asia and causing an annual yield loss of over US$ 600 million. This is because all the modern high-yielding rice varieties are sensitive to complete submergence. A major quantitative trait locus (QTL), SUB1, associated with submergence tolerance, was mapped on chromosome 9 and recently bred into popular rainfed lowland rice varieties sensitive of complete submergence, using marker-assisted backcrossing (MABC). Here, we assessed the impact of introgressing SUB1 into three rice varieties popular in farmers’ fields of South and Southeast Asia, Swarna, Sambha Mahsuri, and IR64, under control conditions as well as following submergence in the field. Under control conditions, no differences were observed between Sub1 introgression lines and their recurrent parents in grain yield or quality aspects. Submergence substantially delayed flowering and maturity, and reduced grain yield, shoot biomass, harvest index, and yield components across cultivars. The reduction in yield was more drastic in the sensitive varieties, particularly when submerged for longer duration (17 d). The significant decline in grain yield was mainly attributed to reductions in grain filling, number of grains per panicle, and grain weight. The SUB1 QTL is effective in conferring tolerance of submergence for about 12–17 d, depending on floodwater conditions. Sub1 introgression lines showed a yield advantage of up to 3.8 t ha⁻¹ and slightly better grain quality after submergence compared with their parents. Apparently, the introgression of SUB1 into popular varieties did not have any negative impact on their performance under control conditions but considerably enhanced their yield and grain quality following short-term submergence.     

Foliar resistance to ozone injury in the genetic base of U.S. and Canadian soybean and prediction of resistance in descendent cultivars using coefficient of parentage

Development of ozone (O₃)-resistant cultivars is a potentially important approach for maintaining crop productivity under future climate scenarios in which tropospheric O₃ pollution is projected to rise. A first step in the breeding of resistant cultivars for a crop such as soybean (Glycine max (L.) Merr.) is identification of sources of O₃ resistance genes. Thirty ancestral lines of soybean were screened for differences in O₃ foliar injury under greenhouse conditions. The ancestors represented 92% of the genetic base of North American soybean as determined by pedigree analysis. Injury among ancestors ranged from 5 to 50% of leaf area, based on response of the five oldest main stem leaves, indicating both the presence of substantial genetic variation for O₃ injury among the ancestors as well as resistance levels greater than that of the standard control cultivar, resistant Essex (15% injury). Ancestral types Fiskeby 840-7-3 and Fiskeby III exhibited the greatest foliar resistance and PI 88788 the least. A subsequent field study confirmed the foliar resistance of the Fiskeby types. Resistant ancestors identified here are proposed for inheritance and DNA mapping studies to determine the genetic basis of foliar resistance. Because the presence of O₃-resistant ancestors suggested that resistant descendents may exist in addition to the resistant control Essex, a method was developed to facilitate their identification. A predicted O₃-resistance score was calculated for 247 publicly-released cultivars, based on pedigree analysis and ancestral response to ozone. Using this approach, the 32 public cultivars most closely related to resistant ancestors and, thus, most likely to be resistant were identified as priority candidates for future screening efforts. Predicted scores from the analysis suggested that cultivars from the Midwest may be more sensitive to foliar injury, on average, than Southern cultivars.