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Cotton aphid (Aphis gossypii Glover) is a worldwide pest of cotton (Gossypium hirsutum L.). High aphid densities visibly damage cotton leaves, reducing leaf photosynthesis and yield. In contrast, lower aphid densities usually do not visibly damage leaves but their effect on photosynthesis is unknown, complicating the decisions on the need for their control. The effect of cotton aphid at lower densities on gas exchange of cotton leaves was investigated under field conditions in the Namoi Valley, Australia. Photosynthesis, leaf area, stomatal opening, and aphid density were assessed on the third mainstem leaf below the terminal of aphid infested and uninfested control plants. Photosynthesis was reduced by a maximum of 27% at a density of 27.6 aphids cm−2 of leaf tissue. Negative linear relationships were found between aphid density and relative photosynthesis, relative conductance and relative transpiration. The temperature of leaves infested with >5 aphids cm−2 was higher than control leaves. Stomatal conductance was reduced faster than photosynthesis, and 87% of stomata on aphid infested leaves were closed, compared to only 34% on control leaves. Closure of stomata was implicated as a cause of reduced photosynthesis in aphid infested cotton leaves. Stomatal closure may be a direct response to cell damage from aphid feeding, as a plant defense or as a response to aphid induced stress. The results suggest that low levels of aphids (e.g., <7 aphids cm−2) on leaves in the upper canopy of cotton crops may be tolerated with low risk to photosynthesis. Core Ideas: Aphis gossypii feeding reduced the photosynthetic rate of cotton leaves which showed no visible damage.Photosynthesis, conductance, and transpiration declined as aphid density increased.Leaves fed on by aphids had a higher percentage of closed stomata than control leaves.Stomatal closure in response to aphid feeding is the likely cause of reduced photosynthesis.Low levels of aphids (e.g., <7 aphids cm−2) may be tolerated with low risk to photosynthesis. [ABSTRACT FROM AUTHOR]

Only a few transcription factors (TFs) regulating which cells of the ovule epidermis differentiate into lint fibres have been identified in cotton (Gossypium hirsutum L.). In this study, the effect on lint yield and fibre quality of over-expressing three TFs in cotton, GhHD-1, GhMYB25 and GhMYB25Like, and their double and triple combinations, were evaluated in field experiments over two seasons. The expression of single or stacked TFs were all driven either by an ovule-specific promoter, FBP 7, or a constitutive promoter, Stunt 7, in a Coker 315 background. TF type, either singly or in combination, was found to be the most significant factor affecting lint yield. Among 64 transgenic lines tested, seven were higher yielding than null segregant lines in one or both seasons and were all from the sets with single and double over-expressed TF combinations. A reduced yield was associated with the set of triple combinations. The two most stable high yielding lines across the seasons recorded 12–22% higher yields than the nulls, although were not competitive to locally adapted commercial controls. Over-expression of TFs singly or in combination did not significantly alter fibre length and strength, but sometimes increased fibre micronaire. There were positive relationships between lint yield and lint percentage and lint yield and fibre density amongst the transgenic lines. Our preliminary results suggest that manipulating TF expression, either singly or in pairs, can increase the density of fibres initiated on developing seeds and fibre yields under field conditions while maintaining overall fibre quality. [ABSTRACT FROM AUTHOR]

Developing and deploying cotton cultivars with high nutrient uptake, use efficiency and tolerance to nutrient related soil stresses is desirable to assist sustainable soil management. Genetic variation, heritability, selection response and quantitative trait loci (QTLs) were investigated for five macronutrients (P, K, Ca, Mg, S) and five micronutrients (Fe, Mn, B, Zn, and Cu) in a recombinant inbred line (RIL) population from an inter-specific cross between Gossypium hirsutum cv. Guazuncho 2, and G. barbadense accession VH8-4602. Na and K/Na ratio were also studied as the imbalance between Na and other nutrients is detrimental to cotton growth and development. The concentrations of nutrients were measured for different plant parts of the two parents and for leaf samples of the whole population collected at early to peak flowering in field experiments over two years in a sodic Vertosol soil. Parental contrast was large for most nutrient concentrations in leaves when compared with other plant parts. Segregation for leaf nutrient concentration was observed within the population with transgression for P, K, K/Na ratio and all micronutrients. Genotypic difference was the major factor behind within-population variation for most nutrients, while narrow sense heritability was moderate (0.27 for Mn and Cu, and 0.43 for B). At least one significant QTL was identified for each nutrient except K and more than half of those QTLs were clustered on chromosomes 14, 18 and 22. Selection response was predicted to be low for P and all micronutrients except B, high for K, Na and B, and very high for K/Na ratio. Correlations were more common between macronutrients, Na and K/Na ratio where the nature and strength of the relations varied (r=-0.69 to 0.76). We conclude that there is sufficient genetic diversity between these two tetraploid cotton species that could be exploited to improve cotton nutrient status by introgressing species-unique favourable alleles. [ABSTRACT FROM AUTHOR]

Crop canopy temperature (Tc) is coupled with transpiration, which is a function of soil and atmospheric conditions and plant water status. Thus, Tc has been identified as a real-time, plant-based tool for crop water stress detection. Such plant-based methods theoretically integrate the water status of both the plant and its environment. However, previous studies have highlighted the limitations and difficulty of interpreting the Tc response to plant and soil water stress. This study investigates the links between cotton Tc, established measures of plant water relations and atmospheric vapour pressure deficit (VPDa). Concurrent measures of carbon assimilation (A), stomatal conductance (gs), leaf water potential (ψ1), soil water (fraction of transpirable soil water (FTSW)) and Tc were conducted in surface drip irrigated cotton over two growing seasons. Associations between A, gs, ψ1, FTSW and Tc are presented, which are significantly improved with the inclusion of VPDa. It was concluded that utilising the strong associations between ψ1, VPDa and Tc, an adjustment of 1.8°C for each unit of VPDa should be made to the critical Tc for irrigation. This will improve the precision of irrigation in Tc based irrigation scheduling protocols. Improved accuracy in water stress detection with Tc, and an understanding of the interaction the environment plays in this response, can potentially improve the efficiency of irrigation. [ABSTRACT FROM AUTHOR]

Exploiting genetic variation through inter-specific breeding has improved cotton yield, fibre properties and adaptability. The objectives of this study were to examine heritability and predicted selection response of yield components and fibre properties in a recombinant inbred line (RIL) population from an inter-specific cross between Gossypium hirsutum (Gh) variety Guazuncho 2, and G. barbadense (Gb) line VH8-4602. A population of 93 and 82 RILs was tested in two seasons, with two parents and local controls, Sicot 75 (Gh) and Sipima 280 (Gb) in field experiments. Seed cotton samples hand harvested before and after defoliation were used to measure lint percent, boll weight, 100 seed weight and the lint to measure fibre length, uniformity, short fibre index (SFI), elongation, strength, micronaire, maturity ratio (MR), percent of maturity (PM) and fineness. There was large phenotypic variation for individual traits and transgressive segregation occurred in lint percent, lint weight/seed, fibre no./seed, uniformity, SFI, elongation, MR and PM. Narrow sense heritabilities were moderate for yield components (34.3-41.2%) and for key fibre properties, length, strength, micronaire and fineness (38.3-42.1%), which led to a predicted selection response of 6.7-24.0% for yield components and 3.9-10.9% for key fibre properties under a selection intensity of 10%. Favourable associations were found between key fibre properties, but an adverse association between lint percent and each of these fibre properties. Only five RILs were identified with desirable combinations. The results demonstrated the value of exploiting inter-specific variation to develop cotton germplasm and how breeding strategies can be improved. [ABSTRACT FROM AUTHOR]

Improving the quality of Australian cotton fiber is essential for maintaining industry viability. Two field experiments were conducted to assess the fiber quality and yarn performance of Australian bred cotton (five Gossypium hirsutum L. and one G. barbadense L.) genotypes. The work included the novel measurement of fiber maturity ratio, fiber linear density, and fiber diameter (ribbon width). The strongest yarns were produced using genotypes with the longest and finest fiber, for example, the strength of 20 tex yarns for the G. barbadense L. cultivar Sipima 280 (length = 36.6 mm, linear density = 143 mtex, ribbon width = 13.7 μm) was 25.4 cN tex-1 cf. the G. hirsutum L. cultivar Sicala 350B (length = 32.5 mm, linear density = 185 mtex, ribbon width = 14.5 μm) yarn strength of 18.1 cN tex-1. Micronaire was an inferior indicator of yarn performance, for example, the G. hirsutum L. breeding lines CHQX12B and CHQX377 each had micronaire values of 4.4, but CHQX377 spun stronger yarns due to its finer and more mature fiber. Lint cleaning had the greatest influence on nep (fiber knot) generation for G. hirsutum L. genotypes, generating on average 104 neps g-1 per lint cleaner passage. There was a negative association between fiber quality and yield, and a cost benefit analysis showed that fiber yield was the dominant economic factor compared to price premiums for better fiber quality. Alternative methods of determining fiber fineness will improve the value of Australian cotton. [ABSTRACT FROM AUTHOR]

Cotton fibers are trichome cells composed primarily of cellulose. Mature fibers have more cellulose and a greater degree of cell wall thickening, and perform better than less mature fibers during textile processing. An automated polarized light microscope instrument called Siro- Mat that measures cotton fiber cell wall thickening was employed to assess the maturity of developing fibers from single cotton fruit. Fruit were taken from the first fruiting branch and position on glasshouse grown Gossypium hirsutum L. (Upland) and G. barbadense L. (Pima) plants, sequentially harvested from 24 days postanthesis (dpa) at approximately four-day intervals up until approximately 50 dpa. The instrument assessed an average of 13,000 fiber snippets per fruit. Upland fibers matured at a slower rate than Pima fibers up to 35 dpa. However, after 45 dpa Upland fibers had achieved a higher average maturity (i.e. 0.99 birefringence maturity index (BMI), cf. 0.79 for Pima). For both species the uniformity of fiber maturity increased as fibers matured up until 35 dpa for Upland and 29 dpa for Pima (i.e. the BMI coefficient of variation decreased as BMI increased during fruit development). It is envisaged that SiroMat will be a useful tool in helping to understand and manage fiber maturity by characterizing the maturation dynamics of cultivars with different inherent fiber properties, and for cultivars subjected to different environmental and agronomic conditions. [ABSTRACT FROM AUTHOR]

Due to an unfortunate misunderstanding, an extra middle initial erroneously appeared in the original publication and the full name of the first author should read Shi Ming Liu. [ABSTRACT FROM AUTHOR]