Commercial Cotton Cultivars Research Articles

SSR marker-assisted improvement of fiber qualities in Gossypium hirsutum using G. barbadense introgression lines

This study demonstrates the first practical use of CSILs for the transfer of fiber quality QTLs into Upland cotton cultivars using SSR markers without detrimentally affecting desirable agronomic characteristics. Gossypium hirsutum is characterized by its high lint production and medium fiber quality compared to extra-long staple cotton G. barbadense. Transferring valuable traits or genes from G. barbadense into G. hirsutum is a promising but challenging approach through a traditional interspecific introgression strategy. We developed one set of chromosome segment introgression lines (CSILs), where TM-1, the genetic standard in G. hirsutum, was used as the recipient parent and the long staple cotton G. barbadense cv. Hai7124 was used as the donor parent by molecular marker-assisted selection (MAS). Among them, four CSILs, IL040-A4-1, IL080-D6-1, IL088-A7-3 and IL019-A2-6, found to be associated with superior fiber qualities including fiber length, strength and fineness QTL in Xinjiang were selected and backcrossed, and transferred these QTLs into three commercial Upland cotton cultivars such as Xinluzao (XLZ) 26, 41 and 42 grown in Xinjiang. By backcrossing and self-pollinating twice, five improved lines (3262-4, 3389-2, 3326-3, 3380-4 and 3426-5) were developed by MAS of background and introgressed segments. In diverse field trials, these QTLs consistently and significantly offered additive effects on the target phenotype. Furthermore, we also pyramided two segments from different CSILs (IL080-D6-1 and IL019-A2-6) into cultivar 0768 to accelerate breeding process purposefully with MAS. The improved lines pyramided by these two introgressed segments showed significant additive epistatic effects in four separate field trials. No significant alteration in yield components was observed in these modified lines. In summary, we first report that these CSILs have great potential to improve fiber qualities in Upland cotton MAS breeding programs.

Prevalence of the Defoliating Pathotype of Verticillium dahliae on Cotton in Central China and Virulence on Selected Cotton Cultivars

AbstractThree hundred and forty‐one isolates of Verticillium dahliae from upland cotton collected from 2007 to 2009 in central China (Hubei, Hunan, Jiangxi, Anhui and Jiangsu provinces) were tested for vegetative compatibility groups (VCGs) and PCR‐based genotyping. Approximately 332 (97%) isolates belonged to VCG1A, whereas the remaining 9 (3%) isolates belonged to VCG2. PCR‐based genotyping also divided the isolates into two groups, namely PCR patterns A and C. There is a complete correspondence between the VCGs and genotypes (VCG1A to PCR pattern A and VCG2 to PCR pattern C). Representative isolates (10 VCG1A isolates, nine VCG2 isolates) were tested for virulence on seedlings of upland cotton (Gossypium hirsutum cultivars E Mian 24 and Yin Rui 361). The VCG1A isolates caused cotton defoliation with the values of the disease severity index and the plant mortality being significantly (P < 0.05) higher than those caused by the VCG2 isolates, which did not cause any defoliation. Two isolates (one of each VCG) were also tested for virulence on 12 popular commercial upland cotton cultivars adapted in central China. Results showed that both isolates, particularly the defoliating pathotype (D pathotype) VCG1A isolate, were virulent on all the tested cotton cultivars. These results suggest that the D pathotype of V. dahliae is widely distributed and has become prevalent in central China.

Germplasm evaluation and transfer of Verticillium wilt resistance from Pima (Gossypium barbadense) to Upland cotton (G. hirsutum)

Verticillium wilt (VW, Verticillium dahliae) is a worldwide destructive soil-borne fungal disease and employment of VW resistant cultivars is the most economic and efficient method in sustainable cotton production. However, information concerning VW resistance in current commercial cotton cultivars and transfer of VW resistance from Pima (Gossypium barbadense) to Upland (Gossypium hirsutum) cotton is lacking. The objective of the current study was to report findings in evaluating commercial cotton cultivars and germplasm lines for VW resistance in field and greenhouse (GH) experiments conducted in 2003, 2006, and 2007. In the study, 267 cultivars and germplasm lines were screened in the GH, while 357 genotypes were screened in the field. The results indicated that (1) VW significantly reduced cotton yield, lint percentage, 50% span length and micronaire, but not 2.5% span length and fiber strength, when healthy and diseased plants in 23 cultivars were compared; (2) some commercial cotton cultivars developed by major cotton seed companies in the US displayed good VW resistance; (3) many Acala cotton cultivars released in the past also had good VW resistance, but not all Acala cotton germplasm are resistant; (4) Pima cotton possessed higher levels of VW resistance than Upland cotton, but the performance was reversed when the root system was wounded after inoculation; (5) VW resistance in some conventional cultivars was transferred into their transgenic version through backcrossing; and (6) some advanced backcross inbred lines developed from a cross between Upland and Pima cotton showed good VW resistance. The successful development of VW resistant transgenic cultivars and transfer of VW resistance from Pima to Upland cotton implies that VW resistance is associated with a few genes if not a major one.

Nodal distribution of free polyamines in cotton ovaries

SUMMARYThe nodal distribution of free polyamines (important regulators of flower induction) in cotton (Gossypium hirsutumL.) ovaries was determined by high-performance liquid chromatography (HPLC). The objective of the study was to investigate the nodal distribution of putrescine (Put), spermidine (Spd) and spermine (Sp) of cotton lines (G. hirsutumL.), and to determine whether there are differences in ovarian polyamine content among three commercial cotton cultivars. A field study was conducted in 2005 and 2006 using the cultivars FM960BR, ST5599BR and DP444BR. Free polyamines Put, Spd and Sp were determined in ovarian tissue of first-position white flowers starting at the beginning of anthesis and collected from the 7th, 9th, 11th and 13th main-stem nodes for four consecutive weeks. There was no significant nodal position by cultivar interaction; thus, the main effects were tested. Put content decreased acropetally along the main stem of the cotton plant with the highest content observed at the 7th node and the lowest at the 13th node. Spd content decreased below and above the 9th node, with the 9th node showing the highest amount of Spd and the 13th node the lowest in both years of the study. Similarly, Sp content decreased below and above the 9th node. In general, the 7th and the 9th node had the highest titre of free polyamines. Among the cultivars tested, FM960BR showed higher polyamine content in one season; however, the observation was not consistent from year to year. The highest amounts of polyamines were observed at the 7th and the 9th node of cotton and this may be associated with the known yield distribution: almost 0·80 of the total yield of cotton is derived from these nodal positions.

Jasmonic acid-induced resistance to the fall armyworm, Spodoptera frugiperda, in conventional and transgenic cottons expressing Bacillus thuringiensis insecticidal proteins

To assess potential interactions between Bacillus thuringiensis Berliner (Bt) proteins and jasmonic acid (JA)-induced resistance to the fall armyworm, Spodoptera frugiperda Smith & Abbot (Lepidoptera: Noctuidae), three commercial Stoneville cotton cultivars, Gossypium hirsutum L. (Malvaceae) (‘ST 475’, a conventional cultivar; ‘ST 4575 BR’, a Bollgard® cultivar expressing Cry1Ac protein; and ‘ST 4554B2RF’, a Bollgard II® cultivar expressing Cry2Ab2 in addition to Cry1Ac), were treated with JA. Two experiments were conducted with 6-day-old S. frugiperda larvae on three cotton cultivars at two phenological stages. The first experiment was conducted under laboratory conditions and used excised cotton leaves; the second experiment was performed under greenhouse conditions on intact cotton plants. Relative growth rates (RGRs) and leaf area consumed by 6-day-old S. frugiperda larvae were determined for each combination of treatments. Overall, JA treatment and cultivars significantly impacted RGR and leaf area consumption. Significant JA treatment*cultivar interactions were observed for RGR of larvae in the laboratory experiment and for leaf area consumption in the greenhouse experiment. An additional experiment evaluated S. frugiperda neonates on the same JA and cotton cultivar combinations (at a single phenological stage) under laboratory conditions. Neonate survival was determined after 3, 5, and 10 days of feeding, and final larval weight after 10 days of feeding. Overall, JA treatment and cultivars significantly impacted final weight and survival of S. frugiperda. Significant JA treatment*cultivar interactions were observed for final weight and on overall survival of S. frugiperda. Combination of the cotton tissue expressing pyramided Bt proteins with JA treatment demonstrated the greatest negative impact on larval development. Apparent synergism between Bt proteins and JA-induced resistance emphasizes that traditional host plant resistance has a role to play in combination with Bt technology.

Genetic divergence among African and American cotton ( Gossypium hirsutum L. race latifolium H.) cultivars and inbred lines through random amplification of polymorphic DNA (RAPD) markers.

Cotton ( Gossypium spp.) is an important cash crop and the second largest source of textile fiber and edible oil throughout the world. This study was conducted to investigate the genetic divergence through random amplified polymorphism (RAPD) molecular markers among the introduced African and American cultivars and inbred lines of cotton ( Gossypium hirsutum L. raca latifolium H.) in Mozambique. We used 24 RAPD primers that amplified a total of 166 bands, identifying 90.96% of polymorphism. The intra and inter group genetic variability quantification evidenced significant variability of 16.30% between the African and American groups. The highest genetic similarity was observed among the African commercial cotton cultivars, whereas American cultivars and inbred lines were considered the most dissimilar ones. The arithmetic complement of Jaccard, obtained with 151 RAPD molecular markers showed that African cultivars Albar BC853 and STAM 42 were the most similar, while the most dissimilar combinations were TAMCOT Sphinx and ISA 205 followed by TAMCOT Sphinx vs ALBAR BC853 and TAMCOT Sphinx vs REMU 40 combinations. Keywords: Molecular variance analysis, decamer primers, dissimilarity, Gossypium hirsutum , molecular markers.

Stability and adaptability of commercial cotton cultivars (Gossypium hirsutum L. race Latifolium H.) in Mozambique.

Cotton, which is also known as ‘white gold’, is an important crop in many developing countries. The crop yield is dependent on the environment in which it is grown. One of the major challenges for cultivar recommendation is the genotype x environment interaction when the performance ranking of genotypes over environments is not constant. The identification of cultivars with high adaptability and stability to the growing conditions is an option to deal with this fact. The objective of the present study was to assess the yield stability and adaptability of commercial cotton cultivars (Gossypium hirsutum L. race latifolium H.) in Mozambique. The experiments were set up over three years in Namialo, Montepuez and Morrumbala, in a total of seven environments. Plots were established in a randomized complete block design with four replications of nine treatments. The stability and adaptability were assessed using methodologies by Annicchiarico and Toler and Burrows. The joint analysis of variance showed that there were high environmental variation and high effect of cultivar x environment interaction. The cultivars ISA 205, STAM 42 and IRMA 12-43 showed greater phenotypic stability for cottonseed yield, according to the Annicchiarico method. Regarding the Toler and Burrows methodology, the cultivar STAM 42 presented specific adaptation to low quality environments, while the cultivar CA 324 presented specific adaptation to high quality environments.

Effect of cotton cultivars on the oviposition preference of pink bollworm (Lepidoptera: Gelechiidae)

The effect of four cotton cultivars on the oviposition behavior of the pink bollworm Pectinophora gossypiella (Saunders) was studied under laboratory and semi-field conditions. Young plants and bolls from four commercial upland cotton cultivars (Lachata, Macnair-220, Midas and Sandra) cultivated in the area of Thessaloniki were used. The four cultivars had palmate leaves, and nectaries on both leaves and bolls. Differences were observed in the trichome density and the length of leaf petiole among the cultivars. The typical shape of bolls was either round or ovate. Differences were observed among the cultivars tested in boll size and bract’s length. In a series of experiments we recorded the number of eggs oviposited in no-, two-, three-, and four-choice tests using either young plants or bolls. Although the four cotton cultivars exhibited a variation in morphological characteristics, the mean number of eggs oviposited on young plants and bolls did not differ among them in two-, three-, and four-choice experiments. Substantially higher number of eggs were oviposited on either young plants or bolls of Midas in no-choice experiments. Eggs were oviposited mainly on newly developed unfolded leaves of the young plants and under the calyx of the bolls. In a semi-field experiment, we found a clear oviposition preference for bolls compared with plant terminals in all the cultivars tested. Females oviposited similar number of eggs in the four cultivars. We discuss the effect of morphological characteristics of cotton cultivars on the oviposition behavior of pink bollworm.

Genetical and biological control of cotton ashy stem caused by Macrophomina phaseolina in outdoor pot experiment

Two outdoor pot experiments were carried out to evaluate the reaction of 11 commercial Egyptian cotton cultivars Macrophomina phaseolina, the incitant of ashy stem in cotton and to evaluate the antagonistic ability of 27 isolates of Trichoderma sp. against pathogen cotton cultivars Giza 85, Giza 87, Giza 89 and Giza 90 were resistant to M. phaseolina because both survival and plant height of these cultivars was not affected when the soil was infested with the pathogen. None of the cultivars were found to be immune to highly pathogenic of M. phaseolina isolate. Of the 27 isolate’s of Trichoderma that were evaluated, the best antagonistic performance was given by isolates nos. 2, 10, and 16 were promising for commercialization because they significantly increased survival and improved plant height and dry weight of the surviving cotton seedlings.

Effects of Varying Planting Dates and Tillage Systems on Reniform Nematode and Browntop Millet Populations in Cotton

Cropping practices that reduce damage from reniform nematode (Rotylenchulus reniformis) and browntop millet (Urochlora ramosa) are needed for improved cotton (Gossypium hirsutum) management. The impacts of early planting dates and reduced tillage systems on these pests were investigated from 2005 to 2007. Planting dates (April 1 or May 1) and tillage systems (conventional or minimum-tillage) were evaluated on four commercial cotton cultivars in a field study at Stoneville, MS. Despite some variability in early-season root infection, reniform nematode soil populations were not affected by any of the treatments. Thus, it appears that neither the tillage practices nor the planting dates examined in this study should be recommended for inclusion in a reniform nematode management program at this time. Mid- and late-season browntop millet pressure was greater in minimum-till plots and in plots planted early. More effective season-long suppression of browntop millet was associated with the traditional planting date and conventional tillage system, so these production practices could benefit producers who need to manage this weed. Accepted for publication 9 November 2010. Published 27 December 2010.

Diallel analysis of upland cotton cultivars

Crosses involving eight commercial upland cotton cultivars were performed in all possible combinations togenerate 28 hybrids. The eight parental genotypes were also evaluated. A field experiment was conducted using a triple Laticedesign (6 x 6) in Itumbiara, Brazil, during the 2000/01 growing season. Data of the following agronomic and fiber traits werecollected: seedcotton yield, lint yield, seed index, picked lint percent, index of production and earliness, micronaire index, fiberstrength, fiber length, uniformity index, short-fiber index, fiber elongation, CSP index, reflectance and yellowness and used inthe analysis of variance as proposed by Griffing (1956), method 4. Significant differences were detected among treatments andthe estimates of combining abilities. Additive gene action prevailed for most traits studied. Both positive and negative heteroticvalues were detected, demonstrating the potential of hybrid combinations for trait improvement in breeding programs.

Response of Commercial Cotton Cultivars to Fusarium solani

Twenty-nine isolates of Fusarium solani, originally isolated from diseased cotton roots in Egypt, were evaluated for their ability to cause symptoms on four genetically diverse cotton cultivars. Analysis of variance showed highly significant variance among cultivars, and isolates as well as the isolate x genotype interactions were highly significant(p < 0.0001). Although most isolates showed intermediate pathogenicity, there were two groups of isolates that showed significant differences in pathogenicity on all four cultivars. None of the cultivars were found to be immune to any of the isolates. On all cultivars, there were strong significant positive correlations between dry weight and each of preemergence damping-off, survival, and plant height. Considering 75% similarity in virulence, two groups comprising a total of 29 isolates were recognized. Ninety-three percent of the isolates have the same pathogenicity patterns with consistently low pathogenicity, and narrow diversity of virulence. Isolates Fs4 and Fs5 shared the same distinct overall virulence spectrum with consistently high pathogenicity. There was no clear-cut relationship between virulence of the isolates based on reaction pattern on 4 cultivars and each of host genotype, previous crop, and geographic origin.

Resistance to silverleaf whitefly, Bemisia argentifolii (Hem., Aleyrodidae), in Gossypium thurberi, a wild cotton species

Abstract Gossypium thurberi Todaro is a wild cotton species native to Mexico and parts of the southwestern USA. Four years of field studies in California's Imperial Valley revealed consistent very high levels of resistance in G. thurberi against silverleaf whitefly, Bemisia argentifolii Bellows and Perring, an important pest of cotton in many regions of the world. Naturally developing field infestations in plots of G. thurberi were significantly lower than in plots of the commercial cotton cultivars DP 5415, Siokra L23, and Stoneville 474. Gossypium thurberi has two morphological traits that, in past research, have been associated with lower levels of whitefly susceptibility: smooth‐ and okra‐leaf; however, the levels of resistance observed in G. thurberi were significantly greater than in the cotton cultivar DP 5415, which is a smooth‐leaf cotton, and Siokra L23 which, like G. thurberi, has both smooth‐ and okra‐leaf traits. Therefore, the high level of resistance in G. thurberi seems to be due to factors above and beyond smooth‐ and okra‐leaf. Siokra L23, which is among the least whitefly‐susceptible cotton cultivars, developed whitefly populations over 30 times those on G. thurberi in all 3 years that Siokra L23 was tested. The difference in whitefly population development between G. thurberi and the other two cotton cultivars was even more striking, up to a 475‐fold difference. In contrast to the clear results on naturally developing field infestations, experiments comparing nymphal survival among G. thurberi and commercial cotton cultivars did not detect antibiosis, and both choice and no‐choice oviposition experiments did not detect antixenosis. Thus, the mechanisms of resistance in G. thurberi remain unknown.

Performance of cotton aphid Aphis gossypii (Hemiptera: Aphididae) lineages on cotton varieties

The performance of three clonal lineages of Aphis gossypii Glover originating from central Greece was studied on six commercial cotton cultivars that differ with respect to leaf pubescence traits (Zeta-2, Zeta-5, Eva, Korina, Acala-SJ2 and Sindos-80). Two main laboratory experiments were conducted: (i) one clonal lineage was studied on all six varieties; and (ii) four varieties were assayed with two other lineages. Aphid development, fecundity, longevity and mortality were recorded and life-table characteristics estimated for all varieties. The results showed that leaf trichome density was significantly correlated with aphid performance (i.e. positive correlation with intrinsic rate of increase and fecundity, and negative correlation with developmental time) in both experiments. Leaf hairiness was at least partly responsible for the poorer performance in cotton aphid lineages. We hypothesise that other factors such as allelochemicals (e.g., gossypol, tannins), which are known to affect hemipteran insects, also might be involved.

Resposta diferencial das cultivares de algodoeiro a Alternaria macrospora

Estudou-se a resposta diferencial de 32 cultivares comerciais do algodoeiro a A. macrospora em casa de vegetação. A inoculação foi realizada em plântulas de 20-25 dias de idade com 25 repetições, utilizando-se o delineamento experimental de blocos ao acaso. As cultivares foram agrupadas através de análise de Scott &amp; Knott. Resistência completa não foi encontrada, sendo que todas as cultivares foram suscetíveis. Houve diferença entre reação de plantas da mesma cultivar. Não obstante, quando algumas plantas das cvs. BRS Antares e Fibermax 986, que mostraram resistência, foram inoculadas com mistura de nove isolados escolhidos ao acaso, as mesmas mantiveram sua resistência a esta mistura. Trabalhos futuros deverão ser realizados para encontrar fontes de resistência a este patógeno em outras espécies de Gossypium.

Variation in Sensitivity Among Some Isolates of Macrophomina phaseolina Isolated from Cotton Roots to Flutolanil Fungicide

Toxicity of the fungicide Flutolanil was in vitro tested against 20 isolates of Macrophomina phaseolina and cotton seedlings of ten commercial cotton cultivars. The isolates were recovered from roots of cotton plants obtained from different cotton-growing areas in Egypt. Most of the tested isolates were sensitive to Flutolanil; however, they varied in sensitivity. Twenty-five percent of the isolates were highly sensitive where IC50 ranged from < 1 to 5.1 μg/ml, 20% of the isolates were sensitive where IC50 ranged from 15 to 30 μg/ml, 45% of the isolates were moderately sensitive where 1C50 ranged from 46 to 58.5 μg/ml, and 10% of the isolates were not much sensitive (tolerant) where 1C50 was > 100 μg/ml. Flutolanil was very safe on both shoots and roots of the tested eultivars (1C50 > 100 μg/ml). Treating cotton seeds with Flutolanil resulted in highly significant (P < 0.01) reductions in pathogenicity of 18 isolates and a significant reduction (P < 0.05) in pathogenicity of isolate M29. M1 was the only isolate, which was insensitive to the application of Flutolanil. In vivo toxicity to Flutolanil was not correlated with its in vitro toxicity. However, a highly significant correlation (r = 0.60, P < 0.01) was observed between pathogenicity of isolates and the in vivo toxicity of the fungicide.

Molecular Marker Diversity and Field Performance in Commercial Cotton Cultivars Evaluated in the Southwestern USA

Genetic diversity in modern upland cotton cultivars (Gossypium hirsutum L.) is thought to be narrow, thus limiting genetic advance. Robust information on the genetic relatedness among currently grown cotton cultivars is lacking. The objectives of the present study were to field test a sample of elite commercial cotton cultivars, including many transgenic cultivars representing the major cottonseed companies, and to evaluate their genetic divergence using simple sequence repeat (SSR) markers. Eighty‐eight SSR primer pairs were chosen for genotyping that provided 177 SSRs. Jaccard's genetic similarity coefficients among 24 genotypes ranged from 0.694 to 0.936, with an average of 0.772, indicating that sufficient genetic diversity does exist within our sample of commercial upland cotton. Genetic similarities among cultivars from the same seed companies were generally higher than the mean of all cultivars and grouped into six major groups: two Deltapine (DP), one Stoneville (ST), one FiberMax (FM), and two New Mexico (NM) Acalas. One California Acala cultivar of New Mexico origin, developed by Phytogen (PHY), did not group with New Mexico Acala germplasm. Texas High Plains stripper type cultivars were distant from picker types and formed independent groups. Under New Mexico growing conditions, DP and ST cultivars yielded higher but produced lower fiber quality, while NM Acala cotton had lower yield but higher fiber quality. The PHY and FM cultivars were intermediate in cotton yield and fiber quality. Six SSR markers were identified to be significantly correlated with fiber yield or quality among the cultivars tested, providing impetus to validate the marker–trait associations.

Genetics and the conservation and use of Australian wild relatives of crops

Genetical research stands to make crucial contributions to the in situ conservation of wild Australian relatives of crop plants, management of their ex situ germplasm collections, and their use in crop improvement. For instance, population genetic theory is basic in formulating collecting strategies. Results from the neutral allele model indicate that allelic richness in samples from equilibrium populations is, although directly proportional to the population size, proportional to the logarithm of the sample size. Such trends underline the importance of dividing the sampling effort among many populations. Our empirical genetical studies have been in the Australian wild relatives of soybean and cotton. These species not only contain significant genetic resources for improving their related crops, but also may be at risk from unwanted hybridisation. In perennial Glycine species, previous cytological and genetic research detected major races within the G. tabacina polyploid complex. A maternal phylogeny on the basis of chloroplast restriction-site variation defined plastome lineages and clarified the evolution of the polyploid complexes. Ongoing research with nuclear sequences focuses on the relationship between chloroplast and nuclear phylogenies and morphology. In Gossypium, estimates of interspecific hybrid fertility and outcrossing rates in natural populations near current cotton crops point to negligible risk of transgene escape from genetically engineered commercial cotton cultivars.

Production of fertile hybrid germplasm with diploid Australian Gossypium species for cotton improvement.

The 17 wild Australian Gossypium species are distant diploid relatives of the commercial tetraploid cottons, G. barbadense L. and G. hirsutum L. They interest cotton breeders as a source of terpenoid-aldehyde-free seeds, a trait only found in five Australian Gossypium species. They elicit further interest because some species grow near current and projected cotton growing areas in Australia and thus could serve as unintentional recipients of transgenes from genetically engineered cotton cultivars. The utility of the wild Australian Gossypium species in cotton breeding depends on the ability to generate fertile hybrids, and to the extent this is possible under glasshouse conditions, it allows predictions regarding the probability that fertile hybrids between the transgenic cottons and spatially associated populations of wild species will arise without human manipulation. The Australian Gossypium species fall into three morphologically and cytologically distinct groups designated the C, G, and K genomes, The G-genome species hybridize most readily with G. arboretum (a diploid A-genome cultivated cotton), while the C- and K-genome species are more compatible with G. hirsutum (a tetraploid AD-genome cultivated cotton). These intergenomic hybrids are sterile, and the chromosome complement of the hybrids must be doubled prior to backcrossing to G. hirsutum. The only exceptions were four G. hirsutum × K-genome triploids, which exhibited limited female fertility when backcrossed to G. hirsutum. Two of the three diploid species geographically associated with commercial cotton fields (G. australe F. Mueller & G. rotundifolium Fryxell, Craven & Stewart) failed to produce hybrid progeny when pollinated with G. hirsutum pollen; the third species (G. sturtianum J.H. Willis) produced only 5 sterile triploids from 25 pollinations. Thus, the probability that wild species could serve as recipients of transgenes is functionally zero, especially in conjunction with the profound prezygotic barriers that separate the cultivated tetraploid cottons from their wild Australian relatives. Eighteen new fertile synthetic polyploids and 23 self-fertile derivatives of two synthetic hexaploids were produced. Synthetic tetraploids require greater effort to backcross than do synthetic hexaploids. These fertile hybrids represent a new avenue of introgression of genes from wild Australian Gossypium species into commercial cotton cultivars, an avenue limited only by the level of recombination.

Performance of Commercial Cotton Cultivars under Elevated Densities of Tobacco Budworm

AbstractThe development of improved cultivars is essential for continued economic production of cotton, Gossypium hirsutum L. Information is limited on how different cotton cultivars compare under elevated densities of tobacco budworm, Heliothis virescens (F.), an economically important cotton pest. Seven field tests were conducted between 1988 and 1992 to evaluate cotton cultivars grown under elevated densities of tobacco budworm (TBW). Cultivars were grown under two regimes: (i) artificial elevated infestation, w/TBW, and (ii) elimination of tobacco budworm, w/o TBW. Elevated densities of TBW (w/TBW) significantly reduced yields compared with w/o TBW, but reduction varied among years and tests. The regression equation for lint yield w/TBW on lint yield w/o TBW was Y = −111.0 + 0.6X. Thus, for every 1.0 kg of lint yield increase per hectare due to cultivar improvement, the corresponding increase under artificial TBW infestation was only 0.6 kg. The regression coefficient for lint percentage on lint yield w/o TBW was Y = 30.85 + 0.006X. These data show that cotton breeders have developed high‐yielding cultivars, but that progress is still needed in the development of resistance to the tobacco budworm injury. They also show that, as cultivars with higher yield potential were developed, these cultivars were better able to tolerate damage by the tobacco budworm. The parity between yield increase per se and yield under elevated densities of tobacco budworm is not 1.0:1.0, but rather 1.0:0.6. This is a useful and practical level of parity.