Screening Of Germplasm Research Articles

واکنش ژنوتیپهای چند جوانه چغندرقند به تنش شوری

با وجود توسعه کشت مکانیزه و استفاده از ارقام منوژرم چغندرقند در کشور، هنوز در برخی مناطق مانند اراضی دارای تنش شوری و خشکی، استفاده از ارقام چند جوانه به منظور کاهش اثرات سوء محیط و افزایش درصد سبز و استقرار توصیه می‌شود. لذا بررسی ژرم‌پلاسم چند جوانه‌ای چغندرقند تحت تنش شوری ضروری بوده تا بتوان در آینده به ارقام چند جوانه متحمل به شوری دست یافت. برای این منظور، 20 گرده افشان مختلف ابتدا در آزمایشگاه در شرایط بدون تنش و شوری 20 دسی زیمنس برمتر به صورت آزمایش فاکتوریل در قالب طرح کاملا تصادفی با چهار تکرار در دو آزمایش جداگانه از نظر درصد جوانه‌زنی بین کاغذ و روش سریع جوانه‌زنی در ارلن با هم مقایسه شده و سپس در محیط گلخانه در شرایط بدون تنش و شوری 16 دسی زیمنس بر متر با چهار تکرار مورد آزمون قرار گرفتند. نمونه‌برداری حدود دو ماه بعد از اعمال تنش در مرحله هشت برگی (استقرار) انجام وعملکرد تر و خشک اندام هوایی و ریشه و عناصر سدیم و پتاسیم و کربوهیدرات محلول اندازه‌گیری شد. از نظر شاخص پتانسیل ظهور در مزرعه، ژنوتیپ‌های 7233، AMP2 و PB13-S2-151-HSF-915 به ترتیب با مقادیر 0.176، 0.09 و 0.05 دارای بیشترین مقدار این شاخص بودند. شوری باعث کاهش وزن خشک کل، اندام هوایی و ریشه، پتاسیم و کربوهیدرات محلول به ترتیب حدود 20، 24و 6، 42 و 38 درصد و افزایش مقدار سدیم و فسفر برگ به ترتیب حدود 4 برابر و 11 درصد شد و در نهایت ژنوتیپ‌های PB13-S2-151-HSF-915، 7233، S1–930882، S1–931008، Poly8823، S1–930770، Gazale، S1–930910، 5RR-87-HS-28 و S1–930792 بر اساس مجموع صفات جوانه‌زنی به روش سریع و روش بین کاغذ، صفات عملکردی و بیوشیمیایی به عنوان ده ژنوتیپ برتر در تنش شوری انتخاب شدند

Phenomics: Approaches and Application in Improvement of Vegetable Crops

Increasing consumption of food, feed, fuel and to meet global food security needs for the rapidly growing human population, raise the necessity to breed high yielding crops that can adapt to the future climate changes, particularly in developing countries. To solve these global challenges, novel approaches are required to identify quantitative phenotypes and to explain the genetic basis of agriculturally important traits. These advances will facilitate the screening of germplasm with high performance characteristics in resource limited environments. High-throughput phenotyping platforms have also been developed that capture phenotype data from plants in a non-destructive manner. In this review, we discuss recent developments of high throughput plant phenotyping infrastructure including imaging techniques and corresponding principles for phenotype data analysis. Phenomics is a way of speeding up phenotyping with the help of high-tech imaging systems and computing power. It has been a practice in plant breeding for selecting the best genotype after studying phenotypic expression in different environmental conditions and also using them in hybridization programs, to develop new improved genotypes.

Recent Advances in Onion Genetic Improvement

Onions are one of the most important vegetable crops worldwide. However, their production faces many challenges. Genetic improvement is one mechanism to address those challenges. In this review, we discuss recent research pertaining to the diseases Fusarium basal rot and Iris yellow spot, the insect pest onion thrips, onion pungency, and dormancy. Recent research for screening onion bulbs for Fusarium basal rot resistance has resulted in improved screening techniques and germplasm exhibiting less disease when inoculated with the disease-causing pathogen. Improved screening methods have resulted in germplasm exhibiting fewer and less severe Iris yellow spot symptoms when onion thrips and conducive environmental conditions are present. Onion germplasm with less and differing compositions of epicuticular wax on their leaves have shown a nonpreference for thrips feeding and have the potential for developing thrips tolerant cultivars. Conventional breeding efforts and genetic manipulation of the genes producing alliinase and lachrymatory factor synthase has resulted in low pungency, tearless onions. In long-day onions, an annual generation time has been achieved by artificially breaking bulb dormancy early while ensuring proper vernalization has been completed. Genetic improvement of these and many other onion traits will continue and result in better production in the future.

Temperate testers’ efficiency in the screening of tropical and subtropical maize germplasm

Despite much effort, little exotic germplasm has been introduced in temperate maize breeding programs. Tropical and subtropical maize germplasm from CIMMYT is the most genetically diverse in the world and should be useful in widening the genetic base of temperate maize germplasm. Extracting the most suitable material from exotic germplasm is a tough challenge for plant breeding programs. This study aimed to determine the optimal number of testers to screen a maize line derived from tropical and subtropical CIMMYT germplasm. For this purpose, four temperate maize testers (MO17, B73, K47/3, and K18) and nine lines from CIMMYT were crossed. The 36 crosses along with two hybrid checks were assessed in a randomized complete block design with three replications at four maize growing regions in Iran. The GGE biplot procedure and methodology proposed by Fan et al. (2010) were used to analyze the results indicating a possibility of direct use of 2, 3, 4, and 9 CIMMYT lines to improve grain yield in temperate environments. Temperate maize testers B73 and K47/3, which belong to the Reid Yellow Dent heterotic group, were very efficient in selecting superior tropical and subtropical CIMMYT germplasm, whereas testers MO17 and K18 from the Lancaster Sure Crop heterotic group were fairly good and weak, respectively. Actually just one temperate tester could select most, if not all, of the top exotic tropical and subtropical lines, and a second tester would provide backup.

Protocol for salt stress screening of African marigold under hydroponic system

The present study was carried out at ICAR-IARI to standardize the protocol for screening of African marigold against saline stress under hydroponic system. Seedlings of African marigold cv. Pusa Narangi Gainda were grown under hydroponics system. They were treated with different levels of NaCl, viz. 0 mM 50 mM, 80 mM, 100 mM, 120 mM, 140 mM, 150 mM, 160 mM, 200 mM, after 7 days of transplanting to standardize the threshold level for the further rapid screening of germplasms at nursery stage. Observations on mortality, growth, morphological, physiological, biochemical parameters and tissue nutrient status were recorded and found to decrease with increasing in saline stress. Mortality in seedlings was not observed up to 80 m M NaCl stress. 150-160 mM qualified as the indicator concentration for the screening of African marigold genotypes based on the performance of marigold genotypes with regard to different morphological, physiological, biochemical parameters and tissue nutrient contents.

Molecular markers and field based screening of wheat germplasm for leaf rust resistance

Molecular markers and field based screening of wheat germplasm for leaf rust resistance

Screening of capsicum germplasm for resistance against Phytophthora capsici causing leaf blight and root rot

Eighty six lines of capsicum were screened for resistance against leaf blight and root rot disease caused by Phytophthora capsici during 2018 by adopting detached leaf and seedling inoculation method, respectively. Out of 86 lines, six lines namely KTC-148, KTC-149, KTPL-19, Chilli Local, Pant Chilli and PBC-631 were found resistant by evaluating 14 days old pepper seedlings grown in poly trays containing peat mixture.Whereasthree lines viz., KTC-144, KTC-148 and PBC-631 were found resistant, when evaluated with detached leaf inoculation method while Chilli Local, KTPL-19 and Chilli Pant were found to be moderately resistant.

Effective medicinal ingredients and screening of excellent germplasm in Rubus chingii

In order to provide rationale for selection of good germplasm in Rubus chingii, main effective medicinal ingredients of green fruit such as gallic acid, ellagic acid, kaempferol-3-rutinoside, astragalin and tiliroside were measured using UPLC for the samples collected from Chun'an county of Zhejiang province, and such parameters as soluble solid contents of ripe fruit of some samples were also measured to study variation among individuals and correlation. It has been found that there were differences among individuals in the contents of gallic acid, ellagic acid, kaempferol-3-rutinoside, astragalin and tiliroside, which ranged from 0.010 2%-0.027 4%, 0.089 5%-0.291 1%, 0.010 5%-0.114 8%, 0.005 8%-0.041 2% and 0.010 9%-0.086 3%, respectively, with a CV of 18.60%, 27.02%, 44.23%, 44.17% and 47.29%, respectively. Gallic acid was positively correlated with ellagic acid, but negatively with kaempferol-3-rutinoside and astragalin significantly. Significantly positive correlation existed between kaempferol-3-rutinoside, astragalin and linden glycoside as well as between ellagic acid and fruit shape index of ripe fruit and between linden glycoside and the content of soluble solids. 51.35% of the individuals had a content of soluble solids more than 15%. Therefore, abundant variations have been found among individuals in effective medicinal ingredients in R. chingii, which shows great potential for selection, but only do 7.61% of the individuals meet the requirement of Chinese pharmacopoeia in terms of the contents of effective medicinal ingredients. Therefore, selection could be first performed in terms of fruit shape index of ripe red fruit, followed by the contents of ellagic acid and kaempferol-3-rutinoside measured. The individuals, in which the contents of effective medicinal ingredients don't meet the requirement of Chinese pharmacopoeia, could be considered for the selection in terms of edible fresh fruit.

Development of a robust hydroponic method for screening of sunflower (Helianthus annuus L.) accessions for tolerance to heat and osmotic stress

Hydroponic systems are known to provide a platform for uniform growth conditions until the reproductive stage. However, many plant species, including sunflower, show poor growth and survivability under conventional hydroponic systems due to poor nutrient availability, hypoxia and algal contamination. Thus, we tested various hydroponic systems to select a hydroponic system suitable for screening of sunflower germplasm. Sunflower accessions showed better growth and leaf gas exchange in newly-designed over conventional hydroponic systems. Selected hydroponic systems were further engaged in sunflower accession screening under heat and osmotic stress in a two-pan system (210 cm × 60 cm). Heat stress treatment was applied by growing sunflower germplasm at 42 °C and osmotic stress by adding polyethylene glycol 8000 which decreased the osmotic potential to − 0.6 MPa. There was significant variability among the sunflower accessions for their ability to survive under stress. Accessions such as C-2721 (43%), C-291 (46%) and D-14 (43%) had lower cell membrane injury percentage under osmotic stress and high seedling survivability (60‒80%) under heat stress when compared with susceptible accessions. Moreover, resistant accessions exhibited greater cuticular waxes and root length but lower transpiration losses. The newly designed hydroponic platform proved reliable for the selection of resistant sunflower accessions. Selected parental lines were validated by assessing their hybrids under field trials across two seasons under water and temperature stress during the reproductive phase (autumn). Hybrid H3 obtained by crossing drought and heat resistant parents had the highest seed yield and water use efficiency.

Screening of wheat germplasm for terminal heat tolerance under hyper-arid conditions

Due to intensive cropping system, late planting of wheat is very common which causes plants to suffer due to terminal heat stress. To adapt and mitigate the adverse effect of heat on wheat, researchers want to develop heat-tolerant wheat genotypes. Therefore, a set of 11 germplasms of wheat was sown in normal period (November 25) as well as in late period (December 25) at Instructional Farm of Swami Keshwanand Rajasthan Agricultural University, Bikaner. Various physiological, gas exchange and yield attributes were measured at different crop growth stages. Results showed that days to anthesis (DTA), relative water content (RWC), membrane stability index (MSI), photosynthetic pigments, photosynthetic rate (A), stomatal conductance (gs), internal CO2 concentration (ci), water use efficiency (WUE) and yield attributes were reduced, whereas transpiration rate (E) was increased under late sown as compared to normal. Most of the physiological and yield characters showed superiority (highest/lowest) in germplasm entry no. 26 followed by 43 and 58. Heat susceptibility index (HSI) was the lowest, whereas chlorophyll stability (CSI) and heat tolerance index (HTI) were the highest recorded in entry 26 followed by 43. Heat-tolerant germplasm could be selected on the basis of high RWC, MSI, photosynthetic pigments, CSI, A, gs, ci, WUE, yield components and HTI, and low E and HSI. In the present investigation, entry no. 26 (IC279317), 43 (IC335971) and 58 (IC336816) were found the best suited germplasm under heat stress. These germplasms supposed to carry the heat-tolerant genes and may be used for further heat tolerance breeding.

Screening of germplasm of Gmelina arborea Linn. against infestation of Tingis beesoni Drake and subsequent impact on leaf anatomy

The present study assessed 42 germplasm of G. arborea by field evaluation, preference experiment as well as the biochemical parameters against its key pest insect T. beesoni, and clearly investigated the pest infestation damages in leaves through anatomical study. Secondary metabolites like phenols, flavanoids and terpenoids showed high concentration in clone SYG-11, which is categorized as a tolerant germplasm. The total phenols (r = -0.914) and total terpenoids (r = -0.848) showed strong negative correlation with the level of pest infestation (PI) and medium negative correlation with total flavonoids (r = -0.54). Consequently, secondary metabolites predicted significant variance (p < 0.05) to the pest incidence, whereas phenols, terpenoids and flavonoids showed strong negative correlation with preference experiment (r = -0.99292, r = -0.96665 and r = -0.84771) respectively. Results indicate that the high phenol content along with terpenoids and flavonoids tend to be the reason for high tolerance of clone SYG-11. In addition, the preference experiment through choice and no choice method confirmed the avoidance or less number of insects settling. The anatomical study of infested leaves illustrated the significant injuries in spongy parenchyma and the palisade parenchyma tissues. Tolerant/resistant quality of clones like SYG-11 against T. beesoni could be more helpful to reduce infestation and causality of G. arborea trees in plantation program.

Improvement of diagnostic markers for resistance to Globodera pallida and application for selection of resistant germplasms in potato breeding.

Occurrence of pale potato cyst nematode, Globodera pallida (Stone) Behrens, was first recorded in Japan in 2015. Among several control measures, cultivation of resistant potato (Solanum tuberosum L.) varieties is the most effective in cost and environmental impact. As no G. pallida-resistant varieties have yet been developed in Japan, great emphasis is being placed on screening of germplasm possessing the resistance and development of the resistant varieties. In this study, we first improved previously reported DNA markers linked to the G. pallida resistance loci (GpaIVsadg and Gpa5) and then used these to screen more than 1,000 germplasms to select several candidate germplasms with resistance. We performed inoculation testing on the selected candidates and identified several resistant germplasms to the Japanese G. pallida population. Furthermore, we developed a simultaneous detection method combining three DNA markers linked to G. pallida and Globodera rostochiensis (Wollenweber) Behrens resistance loci. We validated the ability of C237-I marker to select resistant allele of GpaIVsadg and predict the presence of resistance in a Japanese breeding population. Resistant germplasms identified in this study could potentially be used to develop G. pallida-resistant varieties. The marker evaluation methods developed in this study will contribute to the efficient development of resistant varieties.

Genetic and pathogenic variability among Sclerotinia sclerotiorum isolates of rapeseed-mustard

Sclerotinia sclerotiorum causing stem rot is emerging as a serious problem for cultivation of rapeseed-mustard with its appearance in larger proportions. For this study, a total of forty-eight isolates were collected from rapeseed-mustard growing felds of Punjab and adjoining states. Mycelial compatibility studies revealed that 10.4% pairings among isolates from nearby areas were compatible whereas incompatibility was among those from far away regions. Genetic variability studies using SSR primers divided the isolates into four major groups. Based on these, eight representative isolates from different groups were selected for further testing pathogenic variability; which was assessed on introgression lines of Brassica juncea, derived from hybridization with wild crucifers. Results revealed that isolate SsAm was most aggressive whereas SsMk was the least aggressive. Diferences observed in pathogenicity and other characters amongst the isolates advocate the role of pathogen population structure for better and Efficient screening of germplasm and identifying reliable sources of resistance.

Study of drought stress using PEG-6000 on germination stage of sesame germplasm (Sesamum indicum L.) under laboratory conditions

Sesame is a drought tolerant oilseed crop, but it is sensitive to drought at germination stage. This study was conducted to determine the effect of drought stress on germination of Eight hundred twenty nine sesame germplasm. The experiment was conducted in the laboratory of the Project Co-ordinating Unit, All India Coordinated Research Project on Sesame and Niger (Indian Council of Agricultural Research), JNKVV Campus, Jabalpur (MP). Eight hundred twenty nine sesame germplasm and two levels of drought (0.0 (control) and -4.9 bar) were the treatment tested in the experiment. Study of boxplot analysis results which is used to visually summarize and compare groups of data. On considering the values of germination percent were found maximum in SI-1116, followed by IS-158-3-84, PCU-130, PCU134, NIC-17257, NIC-8399-I, S-0534, RJS-194, JLT-8, IS-130, NIC-17868, NIC-7795-A, ES-10-A and EC-138836-A at -4.9 bar and being identified as the most tolerant germplasm among those tested in this experiment. Distinction of significant difference in germination of germplasm in induced water stress suggested that this parameter could be used as criteria in to screen germplasm to identify those most drought stress at germination stage.

Evaluating salinity tolerance in progeny of domestic and wild barley crosses at germination stage

AbstractSalinity is one of the most important challenges facing future global barley (Hordeum vulgare L.) productivity, as it causes major reduction in germination, growth, grain yield, and quality. Screening germplasm for salinity tolerance at germination is vital to breeding programs because germination is the first stage of plant growth and occurs near the soil surface where salt can accumulate in high concentrations. This experiment was conducted to assess salinity tolerance of 249 genotypes (64 diploid (2×) H. vulgare crosses; 174 tetraploid (4×) H. vulgare crosses; and 11 parents) at the seed germination stage. Salinity treatments applied at imbibition included concentrations of 0, 100, 200, and 300 mM salinity and were maintained for 10 d. Analysis of variance of all families indicated significant (P ≤ .001) genotype × salinity interaction for final germination percentage (FG%), corrected germination percentage (CG%), and germination index (GI) at all treatment levels, indicating high genetic variation for salinity tolerance among screened genotypes. The mean of all measured parameters (FG%, CG%, and GI) decreased as salinity concentration increased. These responses can be used to identify genotypes with salinity tolerance at germination. At 300 mM salinity, progenies in 2× Families 1 and 2 were 14.3 and 12.5% saline tolerant, respectively. A total of 29 progenies from 4× families were tolerant to 300 mM treatment at germination. These progenies would have an economic value for improving barley tolerance for salinity.

History of USDA-ARS Cotton Host Plant Resistance and Breeding Research at Mississippi State, MS

Cotton host plant resistance research was initiated with the establishment of the Boll Weevil Research Laboratory in 1960. Laboratory objectives were to conduct research and develop technology that ultimately could be used to eradicate the boll weevil. Early research concentrated on developing techniques and screening germplasm for resistance. A full-scale boll weevil eradication trial began in southern Virginia and eastern North Carolina in 1978 and after initial success the USDA Animal and Plant Health Inspection Service established an eradication program. This led the host plant resistance program to broaden its research into other pests of cotton. During the 1980s, research continued to focus on tarnished plant bug, tobacco budworm, expanding the genetic diversity of cotton, basic genetic and cotton breeding studies. With the development of field infestation techniques for the tobacco budworm, in the 1990s the research team conducted the first field test of Bacillus thuringiensis (Bt) transgenic cotton for resistance. During this time, root-knot nematode research expanded. Cotton fruiting efficiency and distribution of harvestable bolls and the concept of plant mapping were developed. During the 2000s, research expanded with the use of chromosome substitution lines for the introgression of new alleles into Upland cotton. Nematode research remained active during this time. To date, the research program has developed and released more than 800 germplasm lines and four random-mating populations. Scientists in the program have trained more than 60 graduate students and countless others have been mentored. The full impact of the research team will only be revealed with time.

A Note on the Association Between Thecaphora frezzii Infection and Peanut Pod Density

ABSTRACT The time and labor required to hand-screen germplasm are significant obstacles to developing cultivars resistant to peanut smut, but researchers have investigated few alternatives to manual disease evaluations. Although alternative approaches are available for separating materials based upon differences in density, it is unknown how healthy and infected pods differ in density, especially with the varying maturity levels present in real-world samples. For this reason, the pod densities from 13 peanut genotypes were estimated using a sand displacement approach. In addition, disease incidence and severity data were collected from a total of 45 plants representing 15 genotypes varying in resistance to peanut smut. As expected, the results from the pod density analyses showed significant differences between healthy mature and healthy immature pods. However, healthy mature and healthy immature pods were significantly more and less dense, respectively, than both mature infected and immature infected pods. While additional study is needed, it appears that methods employing differences in pod density may be useful for screening germplasm. Analyses of the disease incidence and severity data showed a strong positive correlation between the two disease measures, verifying a previous report. As a result, collecting disease incidence data alone may be sufficient for screening germplasm. These results may assist in developing more efficient phenotyping methods for screening germplasm for peanut smut resistance.

Proline, Total Antioxidant Capacity, and OsP5CS Gene Activity in Radical and Plumule of Rice are Efficient Drought Tolerance Indicator Traits

The success of a plant breeding program is linked with the rapid screening of crop germplasm. In the following study, the germination stage of rice seeds has been examined for the rapid screening of drought-tolerant genotypes. The rice genotypes (10 drought tolerant, 5 moderately drought tolerant, and 5 drought susceptible) were sown in Petri dishes under control and osmotic stress of 15% PEG6000. Data were recorded after four days of sowing for the osmotic stress-induced change in imbibition rate, speed of germination, radical and plumule length, radical and plumule total fresh and dry weight, proline contents, total antioxidant capacity, and malondialdehyde level in radical and plumule of seeds. Moreover, the change in expression of OsP5CS gene was also recorded in one of each drought tolerant, moderately drought tolerant, and drought susceptible genotypes. Under osmotic stress, the level of proline, total antioxidant capacity, and the expression of OsP5CS were increased in drought-tolerant genotypes as compared to moderately drought tolerant and drought susceptible genotypes. While, the change in imbibition rate, speed of germination, radical and plumule length, and fresh and dry weight were not symmetrical in drought tolerant, moderately drought tolerant, and drought susceptible genotypes. In short, the symmetrical change in proline, total antioxidant capacity, and expression of OsP5CS gene within radical and plumule of drought tolerant, moderately drought tolerant, and drought susceptible genotypes can help rapid screening of drought-tolerant rice genotypes.

NIRS Estimation of Drought Stress on Chemical Quality Constituents of Taro (Colocasia esculenta L.) and Sweet Potato (Ipomoea batatas L.) Flours

Taro (Colocasia esculenta (L.) Schott) and sweet potato (Ipomoea batatas (L.) Lam.) are important food crops worldwide, whose productivity is threatened by climatic constraints, namely drought. Data calibration, validation, and model development of high-precision near-infrared spectroscopy (NIRS) involving multivariate analyses are needed for the fast prediction of the quality of tubers and shoots impacted by drought stress. The main objective of this study was to generate accurate NIRS models for quality assessment of taro and sweet potato accessions (acc.) subjected to water scarcity conditions. Seven taro and eight sweet potato acc. from diverse geographical origins were evaluated for nitrogen (N), protein (Pt), starch (St), total mineral (M), calcium oxalate (CaOx), carbon isotope discrimination (Δ13C), and nitrogen isotopic composition (δ15N). Models were developed separately for both crops underground and aboveground organs. N, Pt, St, and M models could be used as quality control constituents, with a determination coefficient of prediction (r2pred) between 0.856 and 0.995. δ13C, δ15N, and CaOx, with r2pred between 0.178 and 0.788, could be used as an informative germplasm screening tool. The approach used in the present study demonstrates NIRS’s potential for further research on crop quality under drought.

Microsphere stem blockage as a screen for nitrogen-fixation drought tolerance in soybean.

Symbiotic nitrogen-fixation of soybean (Glycine max [Merr.] L) commonly decreases in response to soil drying in advance of other plant processes. While a few soybean lines express nitrogen-fixation drought tolerance, breeding for genetic variation is hampered by laborious phenotyping procedures. The objective of this research was to explore the potential of an initial screen for nitrogen-fixation drought-tolerant genotypes based on a possible relationship with xylem-vessel diameter. The hypothesis was that nitrogen-fixation drought tolerance might result from fewer, large-diameter xylem vessels in the stem that are vulnerable to disrupted flow as water deficit develops. The disrupted flow could cause nitrogen products to accumulate in nodules resulting in negative feedback on nitrogen-fixation rate. The proposed screen involved exposing de-rooted shoots to a suspension containing microspheres (45-53 μm diameter) and recording the decrease in transpiration rate as a result of microsphere xylem-blockage. Two soybean populations were tested. One population was progeny derived from mating of two parents with high and low nitrogen-fixation drought sensitivity. A high correlation (R2 =0.68; P < 0.001) was found in this population between decreasing transpiration rate resulting from the microsphere treatment and increasing sensitivity of nitrogen-fixation to soil drying. The second tested population consisted of 16 genotypes, most of which had been previously identified in germplasm screens as expressing nitrogen-fixation drought tolerance. Nearly half of the lines in this second population were identified in the screen as showing minimum blockage of transpiration when exposed to the microspheres. Overall, these results showed the potential of using the microsphere screen to identify candidate genotypes expressing nitrogen-fixation drought tolerance.