Early Seedling Vigour Research Articles

Genes That Mediate Starch Metabolism in Developing and Germinated Barley Grain.

Starch is synthesized in the endosperm of developing barley grain, where it functions as the primary source of stored carbohydrate. In germinated grain these starch reserves are hydrolyzed to small oligosaccharides and glucose, which are transported to the embryo to support the growth of the developing seedling. Some of the mobilized glucose is transiently stored as starch in the scutellum of germinated grain. These processes are crucial for early seedling vigor, which is a key determinant of crop productivity and global food security. Several starch synthases (SS), starch-branching enzymes (SBEs), and starch debranching enzymes (isoamylases, ISA), together with a limit dextrinase (LD), have been implicated in starch synthesis from nucleotide-sugar precursors. Starch synthesis occurs both in the developing endosperm and in the scutellum of germinated grain. For the complete depolymerization of starch to glucose, α-amylase (Amy), β-amylase (Bmy), isoamylase (ISA), limit dextrinase (LD), and α-glucosidase (AGL) are required. Most of these enzymes are encoded by gene families of up to 10 or more members. Here RNA-seq transcription data from isolated tissues of intact developing and germinated barley grain have allowed us to identify the most important, specific gene family members for each of these processes in vivo and, at the same time, we have defined in detail the spatio-temporal coordination of gene expression in different tissues of the grain. A transcript dataset for 81,280 genes is publicly available as a resource for investigations into other cellular and biochemical processes that occur in the developing grain from 6 days after pollination.

Relationship of size and shape rice seed to early seedling vigor traits

Rice crop improvement program for direct-seeded has been directed at identifying the quality of seeds with rapid uniform germination and biomass accumulation during the initial phase of seedling establishment. Seed and embryo size are thought as two critical factors in the emergence of faster and vigorous seedlings. For the reason, this study was purposed to evaluate the relationship between the size and shape of rice seed with embryo size and its effects on germination. This study was designed using rice seeds from 55 genotypes, which were grouped in three sizes (medium, long, and extra-long) and two shapes (medium and slender). Germination was conducted with the top of paper method in a controlled germinator (24h lighting, 25 ± 2°C, 95%). We have found that the size and shape of seed significantly affected (α < 0.05) to embryo length, the time of radicles and plumules emergence, and seedling dry weight. Longer seeds tended to have longer embryos and emerged of radicles and plumules faster. Meanwhile, longer seeds with slender shape tend to have greater seedling dry weight. The results informed that the size and shape of rice seeds could be considered important characters for early seedling vigor traits in direct-seeded systems.

Identification of QTL and candidate genes involved in early seedling growth in rice via high-density genetic mapping and RNA-seq

Early seedling vigor (ESV) is a major breeding target in rice, especially under direct seeding. To identify quantitative trait locus (QTL) affecting ESV, a recombinant inbred line population derived from a cross between 02428 and YZX, two cultivars differing in vigor during early seedling growth, was used for QTL analysis. Nine traits associated with ESV were examined using a high-density map. Of 16 additive loci identified, three were detected in two generations and thus considered stable. Four epistatic interactions were detected, one of which was repeated in two generations. Further analysis of the pyramiding effect of the three stable QTL showed that the phenotypic value could be effectively improved with an increasing number of QTL. These results were combined with results from our previous QTL analysis of the germination index. The lines G58 and G182 combined all the favourable alleles of all three stable QTL for ESV and three QTL for germination speed. These two lines showed rapid germination and strong ESV. A total of 37 candidate differentially expressed genes were obtained from the regions of the three stable QTL by analysis of the dynamic transcriptomic expression profile during the seedling growth period of the two parents. The QTL are targets for ESV breeding and the candidate genes await functional validation. This study provides a theoretical basis and a genetic resource for the breeding of direct-seeded rice.

Effects of fertilizer micro-dosing in nursery on rice productivity in Madagascar

ABSTRACT Currently, most rice farmers in the central highlands of Madagascar do not apply mineral fertilizer in their fields and we investigated whether a fertilizer micro-dose applied to the seedling nursery could serve as an entry point for intensification. Effects of nursery applications of a micro-dose of mineral (P and NPK) or locally produced sources of fertilizers (Guanomad, Vermicompost) on seedling vigour were evaluated, as was final grain yield after transplanting to main fields that were either not fertilized (farmers’ practice) or received combinations of mineral N, P and K fertilizer. Applying only P to the nursery had minor effects and we conclude that early seedling vigor is more limited by N than P, while grain yield in the main field was more limited by P than N. Carry-over effects of the nursery application of NPK and of guano on final grain yield were observed under farmers’ practice and when only urea was applied. The nursery NPK application significantly increased agronomic nitrogen use efficiency of urea application. We conclude that the low cost of micro-dosing NPK in the nursery makes this a profitable option for small-scale farmers cultivating rice on poor-fertility soils. Sole urea application in the main field is not a profitable option but would at least need additional nursery NPK application as an insurance against losing investments in N fertilization. Longer-term sustainability would require direct nutrient inputs into the main plot and additional low-cost nutrient management options should therefore be considered.

Non-destructive phenotyping for early seedling vigor in direct-seeded rice

BackgroundEarly seedling vigor is an essential trait of direct-seeded rice. It helps the seedlings to compete with weeds for water and nutrient availability, and contributes to better seedling establishment during the initial phase of crop growth. Seedling vigor is a complex trait, and phenotyping by a destructive method limits the improvement of this trait through traditional breeding. Hence, a non-invasive, rapid, and precise image-based phenotyping technique is developed to increase the possibility to improve early seedling vigor through breeding in rice and other field crops.ResultsTo establish and assess the methodology using free-source software, early seedling vigor was estimated from images captured with a digital SLR camera in a non-destructive way. Here, the legitimacy and strength of the method have been proved through screening seven diverse rice cultivars varying for early seedling vigor. In the regression analysis, whole-plant area (WPA) estimated by destructive-flatbed scanner (WPAs) and non-destructive imaging (WPAi) approaches was strongly related (R2 > 83%) and suggested that WPAi can be adapted in place of destructive methods to estimate seedling vigor. In addition, this study has identified a set of new geometric traits (convex hull and top view area) for screening breeding lines for early seedling vigor in rice, which decreased the time by 80% and halved the cost of labor in data observation.ConclusionsThe method demonstrated here is affordable and easy to establish as a phenotypic platform. It is suitable for most glasshouses/net houses for characterizing genotypes to understand the plasticity of shoots under a given environment at the seedling stage. The methodology explained in this experiment has been proven to be practical and suggested as a technique for researchers involved in direct-seeded rice. Consequently, it will help in the simultaneous screening of genotypes in large numbers, the identification of donors, and in gaining information on the genetic basis of the trait to design a breeding program for direct-seeded rice.

Genetic diversity in pearl millet restorers based on seed vigour traits and SSR markers

Thirty four pearl millet restorer lines were evaluated on the basis of nine seed vigour traits and molecular analysis was done with 55 SSRs to study the genetic divergence among them. Cluster analysis based on seed vigour parameters revealed the considerable amount of variability and all genotypes were divided into six clusters. Furthermore, a set of 39 SSRs, selected after initial screening of 55, amplified 226 alleles with a mean of 5.84 alleles per locus. The highest polymorphic information content (PIC) value obtained was for PSMP 2084 (0.88) with a range of 0 to 0.88 and average PIC of 0.558. Neighbor joining tree based on molecular data differentiated all the genotypes into two major groups. The grouping based on both approaches can help breeders to use the studied material in further breeding for improvement of germination potential and early seedling vigour of pearl millet.

Identification of quantitative trait loci governing early germination and seedling vigor traits related to weed competitive ability in rice

Weed competitive ability (WCA) is vital for the improvement of grain yield under direct-seeded and aerobic rice ecosystems where weeds are a major limiting factor. Early seed germination (ESG) and early seedling vigor (ESV) are the crucial traits for WCA. This study attempted to map the quantitative trait loci (QTLs) and hotspot regions governing ESG and ESV traits. A total of 167 BC1F5 selective introgression lines developed from an early backcross population involving Weed Tolerant Rice 1 (WTR-1) as the recipient parent and Y-134 as the donor parent were phenotyped for ESG and ESV traits. Analysis of variance revealed significant differences in ESG-related traits except for root length and in ESV-related traits except for plant height at 7 days after sowing. A total of 677-high quality single nucleotide polymorphism (SNP) markers were used to analyze the marker-trait association from a 6 K SNP genotyping array. Forty-three QTLs were identified on all chromosomes, except on chromosomes 4 and 8. Thirty QTLs were contributed by a desirable allele from Y-134, whereas 13 QTLs were from WTR-1. Twenty-eight of the identified genetic loci associated with ESG and ESV traits were novel. Two QTL hotspot regions were mapped on chromosomes 11 and 12. The genomic regions of QTL hotspots were fine-tuned and a total of 13 putative candidate genes were discovered on chromosomes 11 and 12 collectively. The mapped QTLs will be useful in advancing the marker aided-selection schemes and breeding programs for the development of rice cultivars with WCA traits.

Phenotyping and QTL mapping for cold tolerance at the germination and seedling stages in Argentine temperate rice

In Argentina, the yield potential of rice (Oryza sativa L.) under suboptimal temperatures of temperate regions and during early sowing in tropical regions depends on its low-temperature germinability (LTG) and subsequent cold tolerance at the seedling stage (CTS). This study focused on the phenotyping and identification of contrasting henotypes for LTG and CTS of 18 rice genotypes genotyped with 49 markers previously linked to cold tolerance. The selected markers revealed phenotypic variability among the genotypes evaluated. The results also demonstrated that both traits are regulated by different genes and that CTS is associated with differential alleles of candidate gene (CG)-based markers. Biplot clustering analysis allowed the selection of two cultivars, H298a/90 and Puita INTA CL, contrasting for LTG, CTS and CG alleles. An F2 population (n = 128) derived from these two cultivars was genotyped with 43 SSR- and CG-based markers and 89 F2:3 families (~ 1800 seedlings) phenotyped for CTS. Single-marker analysis detected two major QTL that had been previously reported for CTS: qCTS11, which explained 18.35% of the phenotypic variance at 7 days of treatment, and qCTS12, which explained 26.62% and 47.94% of the phenotypic variance at 7 and 14 days of treatment, respectively. Marker-assisted introgression of QTL alleles favorable for CTS into Puita INTA CL, which has high LTG, could contribute to obtaining breeding lines with early seedling vigor adapted to the sowing season in Argentina.

Genetic variability in rice (Oryza sativa L.) landraces for seedling vigour traits

A study was carried out in 73 rice landraces along with two varieties to study the genetic variability and association of the traits related to early seedling vigour. Morphological traits such as seedling height, leaf sheath length and leaf blade length were measured in seedlings on 15 and 25 days after sowing. Analysis of variance indicated the presence of genetic variability for seedling vigour related traits in rice landraces. High GCV, PCV and high heritability coupled with high genetic advance as per cent of mean were observed indicating selection may be effective for improvement of these traits. Estimates of genotypic correlation were higher than that of phenotypic correlation indicating strong genetic association among the traits studied. Landraces viz., Senkar, Palkachaka, Murugankar, Kaatuponni, Kochin Samba, Poongar, Thillainayagam and Kuliyadichan exhibited significantly higher seedling height on both 15 and 25 DAS. These landraces may harbour favourable alleles for early seedling vigour. Hence, they can be utilized for improving early seedling vigour after validating its stable expression across varied environments. &nbsp

Seedling Raising Nursery Business for Sustainable Mechanical Rice Transplanting in the Southern Delta of Bangladesh

Mechanical rice transplanting needs special seedling raising. The Appropriate Scale Mechanization Innovation Hub (ASMIH)-Bangladesh project trained farmers on raising rice seedling. Extensive field trials were conducted during 2017 to 2019 by the ASMIH-Bangladesh and farmers’ groups are now confident to establish seedling nursery on commercial basis. It will solve the seedling raising problem for mechanical transplanting and also increase their income. The main advantages of mechanical transplanting are transplanting of seedlings at the age of 12-30 days with uniform spacing and optimum plant density; higher productivity compared to traditional transplanting where plant spacing and density are not always be consistent; less transplanting shock, early seedling vigor and uniform crop establishment; less time, labor, drudgery and health risks for farm laborers. FAO developed a rural invest software named “RuralInvest” to access the sustainability of rural projects such as mechanization, development projects, entrepreneurial opportunities, investment projects etc. In this study, the RuralInvest software was used to evaluate the seedling raising nursery business. The total time duration of the project was estimated for 5 years with farmer’s own investment where the direct beneficiaries were 08 farmers and indirect beneficiaries were 45 farmers. Two types of seedling raising techniques were evaluated with the RuralInvest software, one for mat-type and another for economy plastic tray-type seedling raising. The IRR, NPV, payback period and Investment per direct beneficiaries were found 29.10%, BDT 2056, 2.46 year, BDT 348.75 and 22.52%, BDT 3834, 2.84 years, BDT 911.25 for mat-type and plastic tray-type seedling raising, respectively. To establish the sustainable mechanization of rice transplanting and meet the challenges of labor crisis during rice transplanting season, seedling raising nursery business would generate sustainable entrepreneurship through income generation and raising seedlings for mechanical rice transplanting in the Southern delta of Bangladesh.

Alteration in plant spacing improves submergence tolerance in Sub1 and non-Sub1 rice (cv. IR64) by better light interception and effective carbohydrate utilisation under stress.

Besides genetic improvement for developing stress-tolerant cultivars, agronomic management may also add considerable tolerance against different abiotic stresses in crop plants. In the present study, we evaluated the effect of six different spacing treatments (S1: 10 × 10 cm; S2: 15 × 10 cm; S3:15 × 15 cm; S4:20 × 10 cm; S5: 20 × 15 cm; S6: 20 × 20 cm (row-row × plant-plant)) for improving submergence tolerance in rice. A high yielding submergence intolerant rice cultivar IR64 was tested against its SUB1 QTL introgressed counterpart (IR64-Sub1) for 12 days of complete submergence for different spacing treatments in field tanks. Relatively wider spaced plants showed higher individual plant biomass and early seedling vigour, which was particularly helpful for IR64 in increasing plant survival (by 150% in S6 over S1) under 12 days of submergence, whereas the improvement was less in IR64-Sub1 (13%). Underwater radiation inside the plant canopy, particularly beyond 40 cm water depth, was significantly greater in wider spacing treatments. Leaf senescence pattern captured by SPAD chlorophyll meter reading and chlorophyll fluorescence imaging data (Fm, Fv/Fm) taken at different time intervals after stress imposition suggested that there was lesser light penetration inside the canopy of closer spaced plants, and that it might hasten leaf senescence and damage to the photosynthetic system. The initial content of total non-structural carbohydrate (NSC) was higher in wider spaced plants of IR64, and also the rate of depletion of NSC was lesser compared with closer spaced plants. In contrast, there was not much difference in NSC depletion rate under different spacing in IR64-Sub1. Further, higher antioxidant enzyme activities in wider spaced plants (both IR64 and IR64-Sub1) after de-submergence indicated better stress recovery and improved tolerance. Taken together we found that wider spacing (row-row: 20 cm and plant-plant: 15 cm and more) can significantly improve submergence tolerance ability in rice, particularly in submergence intolerant non-Sub1 cultivar like IR64, perhaps due to better underwater light penetration, delayed leaf senescence and slower depletion of NSC reserve.

‘DUS’ characterization of an endangered salt tolerant radish landrace (Newar)

In this study, responses to salinity stress of three varieties of radish, viz., ‘Newar’ (landrace), ‘Pusa Mridula’ and ‘White Excel’, were recorded. Additionally, landrace Newar was also characterized for ‘Distinctness, Uniformity and Stability’ (DUS) using 34 descriptors. Results indicated higher salt tolerance in ‘Newar’ as evidenced by relatively early germination and high early seedling vigour than other varieties regardless of the salinity of the irrigation water. Although salinity stress, especially up to 8.0 dS m-1, had no adverse effect on shoot growth in all the varieties, effects on root growth were quite different. While ‘Newar’ exhibited non-significant differences in root fresh weight (RFW) at different salinity levels, ‘White Excel’ displayed nominal variations up to 8.0 dS m-1 salinity and ‘Pusa Mridula’ registered consistent declines in RFW with increasing salinity. ‘Newar’ plants were found to be efficient in Na+ exclusion and in maintaining a favourable Na+ to K+ ratio in their shoots and roots. Further, proline accumulation was much higher in salt treated Newar than in ‘White Excel’ and ‘Pusa Mridula’ plants. Based on DUS descriptors, number of leaves, leaf length, and root length and weight were found to be the major distinguishable characters in Newar.

Transcriptional and biochemical analyses of gibberellin expression and content in germinated barley grain.

Mobilization of reserves in germinated cereal grains is critical for early seedling vigour, global crop productivity, and hence food security. Gibberellins (GAs) are central to this process. We have developed a spatio-temporal model that describes the multifaceted mechanisms of GA regulation in germinated barley grain. The model was generated using RNA sequencing transcript data from tissues dissected from intact, germinated grain, which closely match measurements of GA hormones and their metabolites in those tissues. The data show that successful grain germination is underpinned by high concentrations of GA precursors in ungerminated grain, the use of independent metabolic pathways for the synthesis of several bioactive GAs during germination, and a capacity to abort bioactive GA biosynthesis. The most abundant bioactive form is GA1, which is synthesized in the scutellum as a glycosyl conjugate that diffuses to the aleurone, where it stimulates de novo synthesis of a GA3 conjugate and GA4. Synthesis of bioactive GAs in the aleurone provides a mechanism that ensures the hormonal signal is relayed from the scutellum to the distal tip of the grain. The transcript data set of 33 421 genes used to define GA metabolism is available as a resource to analyse other physiological processes in germinated grain.

Nutripriming with zinc sulphate and borax for early growth and seedling vigour in grain cowpea [Vigna unguiculata (L.) Walp

The experiment was conducted at Coconut Research Station, Balaramapuram with an objective to study the effect of nutripriming with ZnSO4 and borax on the early growth and seedling vigour and Zn and B content in grain cowpea. Nutripriming treatments had significant effect on germination parameters. Nutripriming with ZnSO4 either at 0.025 or 0.05 per cent recorded higher values for the germination parameters. These treatments recorded 19.68 and 18.51 per centage higher germination than control. Germination index was 1.4 times higher in seeds primed with ZnSO4 @ 0.025 and 0.05 per cent and also recorded higher values for mean daily germination and speed of germination. The highest co-efficient rate of germination and germination rate index was recorded by seed priming with ZnSO4 at 0.05 per cent and it was closely followed by ZnSO4 @ 0.025 per cent for 4 h. Nutripriming with ZnSO4 either @ 0.025 or 0.05 per cent recorded the lowest mean germination time and time to reach 50 per cent germination and also recorded higher Zn and B content. Vigour index also followed the same trend. Hence it can be concluded that nutripriming with ZnSO4 either at 0.025 or 0.05 per cent can be recommended for early seedling growth, seedling vigour and higher Zn and B content in grain cowpea.

Genetic potentiality of lowland indigenous indica rice (Oryza sativa L.) landraces to anaerobic germination potential

Poor germination and delayed seedling establishment under flooded soil are the major challenges for the wide adaptation of direct-seeded rice production in both rainfed and irrigated areas. So, in the present study 88 lowland indigenous rice landraces from Koraput, India were evaluated for their anaerobic germination (AG) potential and early seedling vigor traits under flooded soil for two consecutive years. Variations of seed characteristics such as grain size, weight and sugar content along with anaerobic germination as well as early seedling growth parameters were compared with tolerant and susceptible check variety. The morpho-physiological parameters were subjected to principal component analysis (PCA) and cluster analysis. The first five axes of the PCA showed 86.64% of the total variation and indicated large variations among the landraces. Major traits, such as shoot length, root length, fresh weight, dry weight and anaerobic vigor index appeared to be important determinants of phenotypic diversity among the landraces. Three rice landraces (Bausaganthi, Patadhan and Basantichudi) showed superior AG potential compared to check genotypes. In addition, these landraces with higher activity of alcohol dehydrogenase with lower activity of amylase may help them for better seedling establishment underwater. The presence of AG associated primer either RM 3475 or RM 478, with PIC value 0.80 and 0.75, respectively was observed and thus, helpful in evaluating the genetic diversity of studied rice landraces for AG potential. These three landraces showed promising genetic potentiality for AG and could be useful in rice breeding programs.

Mapping of dwarfing gene Rht14 in durum wheat and its effect on seedling vigor, internode length and plant height

Short coleoptiles associated with GA-insensitive Rht-1 alleles in wheat reduces yield due to poor seedling establishment under dry, or stubble-retained conditions. Hence there is a need for alternative dwarfing genes for wheat improvement programs. GA-sensitive dwarfing gene Rht14 confers semidwarf stature in wheat while retaining longer coleoptiles and early seedling vigor. Two RIL populations were used to identify the map position of Rht14 and to estimate its effect on plant height, coleoptile length, seedling shoot length, spike length and internode length. Rht14 on chromosome 6A was mapped in the genomic region 383–422 Mbp flanked by GA2oxA9 and wmc753 in a Bijaga Yellow/Castelporziano RIL population. Recombination events between Rht14 and GA2oxA9 in the RIL population indicated that Rht14 might not be allelic to GA2oxA9. The conserved DNA sequence of GA2oxA9 and its flanking region in Castelporziano also suggested that the point of mutation responsible for the Rht14 allele must be a few Mbp away from GA2oxA9. The dwarfing effects of Rht14 on plant height, internode length and seedling vigor were compared with those of Rht-B1b in an HI 8498/Castelporziano RIL population. Both genes significantly reduced plant height and internode length. Rht-B1b conferred a significant reduction in coleoptile length and seedling shoot length, whereas Rht14 reduced plant height, but not coleoptile and seedling shoot length. Therefore, Rht14 can be a used as an alternative to Rht-B1b for development of cultivars suitable for deeper sowing in dry environments and in conditions of conservation agriculture where crop residues are retained.

Effect of Plant Density, Boron Nutrition and Growth Regulation on Seed Mass, Emergence and Offspring Growth Plasticity in Cotton

Seed nutrients reserves have direct relationship with seed functional traits and influence offspring performance. Effects of plant density, foliage boron (B) nutrition and mepiquat chloride (MC) growth regulation on seed nutrients reserves, seed mass and production, and emergence and offspring growth traits of cotton were studied in two years field experiment. Seed nutrients reserves and seed mass were decreased at higher maternal plant density relative to lower plant density with concomitant decrease in emergence and offspring seedling growth. However, maternal foliage B nutrition and MC growth regulation enhanced seed nutrients reserves, seed mass, emergence and offspring seedling growth performance. There was a significant positive relationship between seed mass and seed nutrients reserves indicating that changes in nutrient availability/uptake in response to maternal ecological factors determine variation in seed functional traits. Nonetheless, seed mass was positively correlated with emergence percentage and negatively with emergence timing. Furthermore, variation in offspring seedling growth traits with seed mass indicated the significance of initial seed nutrients reserves for early seedling vigour and establishment. In conclusion, lower maternal plant density, B nutrition and MC growth regulation ensued in higher emergence and offspring seedling growth of cotton because of higher seed nutrient reserves and seed mass.

Simultaneous mapping of multiple QTLs &amp; complex traits in rice: Association mapping-indispensable for effective molecular breeding

Association mapping or linkage disequilibrium mapping is extensively used in dissecting the genetic nature of many human diseases and now extended to plant system for mapping the complex loci. Association Mapping is a method used to detect QTLs controlling traits based on correlating genotype with phenotype. The main advantage of association mapping is the use of natural variability, relatively less expensive and less time requiring for mapping. The lead lecture includes linkage disequilibrium (LD), its assessment, mapping and generalized scheme for association mapping involving basic steps in mapping a complex trait. The talk also includes the association mapping study on cold stress tolerance, high temperature stress tolerance, early seedling vigour, grain protein content and grain Fe and Zn content in rice performed at National Rice Research Institute, Cuttack, Odisha, India.

Mycorrhizal contribution to phosphorus nutrition of cotton in low and highly sodic soils using dual isotope labelling (32P and 33P)

Little is known about how the adverse physical and chemical environment in sodic soils affects plant-mycorrhizal relationships. We investigated mycorrhizal colonisation and plant nutrient uptake of cotton plants under highly stressed (Exchangeable Na percentage (ESP) 21) and less stressed (ESP 7) conditions with two rates of applied P. The relative hyphal contribution to P uptake was quantified using dual isotope labelling techniques (32P and 33P). Root colonisation and P uptake of mycorrhizal cotton plants reduced by 16% and 20%, respectively, in highly sodic soil as compared to plants in low sodic soil, however, the relative proportion of P delivered via hyphal pathways (32P from root-free hyphal compartment) was similar. Under high P conditions, the relative increase in the proportion of 33P (root + hyphae compartment) taken up by inoculated plants was greater in the low sodic soil relative to the high sodic soil. Mycorrhization improved early seedling vigour, and nutrient uptake. Reduced colonisation and hyphal exploration of the soil, possibly due to the physical and chemical constraints imposed by highly-sodic soil, rather than poorer mycorrhizal function, may be responsible for limited early P uptake of cotton in highly-sodic soil.

Interactive effects of carbon dioxide, low temperature, and ultraviolet-B radiation on cotton seedling root and shoot morphology and growth

Interactive effects of multiple environmental stresses are predicted to have a negative effect on cotton growth and development and these effects will be exacerbated in the future climate. The objectives of this study were to test the hypothesis that cotton cultivars differ in their responses to multiple environmental factors of (CO2) [400 and 750 µmol·mol–1 (+(CO2)], temperature [28/20 and 20/12°C (–T)], and UV–B radiation [0 and 10 kJ·m–2·d–1 (+ UV–B)]. A genetic and molecular standard (TM-1) and three modern cotton cultivars (DP1522B2XF, PHY496W3R, and ST4747GLB2) were grown in eight sunlit, controlled environment chambers with control treatment 400 µmol·mol–1 [CO2], 28/21°C temperature, and 0 kJ UV–B. The results showed significant differences among the cultivars for most of the shoot and root parameters. Plants grown under low temperature alone or as a combination with + UV–B treatment caused more detrimental effects on root and shoot vigor. Although the elevated CO2 treatments weakened the damaging effects of higher UV–B levels on cotton growth on all cultivars, increased CO2 could not mask the negative effects of low temperature. When comparing all cultivars, genetic standard TM-1 produced the smallest values for the majority of traits under CO2, UV–B, and low temperature either alone or in combination with other treatments. Based on principal component analysis, the four cultivars were classified as tolerant (DP1522B2XF), intermediate (PHY496W3R and ST4747GLB2) and sensitive (TM-1) to multiple environmental stresses.Low temperature was identified as the most damaging treatment to cotton early seedling vigor while elevated CO2 caused the least. Existing variability of cotton cultivars in response to multiple environmental stresses could allow for selection of cultivars with the best coping ability and higher lint yield for future climate change environments.