Bemisia tabaci (Hemiptera: Aleyrodidae) biotype B colonisation and leaf morphology relationships in upland cotton cultivars

Cultivars of upland cotton, Gossypium hirsutum L., are widely grown throughout the world for fibre production. They are also good reproductive hosts for Bemisia tabaci (Gennadius) biotype B. We studied the relationships between cotton leaf morphology and whitefly population densities in eight United States Deltapine and six Australian cotton cultivars and breeding lines at Holtville, California, in 1996. Results showed that okra-leaf cultivars and lines were colonised with fewer whitefly adults, eggs and nymphs compared to normal-leaf cultivars. The distance from underleaf surfaces of cotton leaves to the centres of nearest minor vascular bundles was negatively correlated with whitefly adult, egg and nymphal densities on leaves for all genotypes with the exception of the Australian breeding line 89013–114. Our results suggest that okra-leaf and distance from underleaf surfaces to the centre of nearest minor vascular bundles of cotton leaves are genetic traits that have potential for breeding whitefly-resistant upland cotton cultivars.     

Bemisia tabaci (Homoptera: Aleyrodidae) biotype B colonization on okra- and normal-leaf upland cotton strains and cultivars

We compared smooth-leaf okra- and normal-leaf upland cotton (Gossypium hirsutum L.) strains and cultivars for susceptibility to colonization by Bemisia tabaci (Gennadius) biotype B. Experiments were conducted at seven field sites, five at Holtville, CA, and two at Maricopa, AZ, during 1996-2000. Okra-leaf strains and cultivars, as a group, had lower numbers of adults, eggs, and nymphs compared with normal-leaf strains and cultivars indicating the potential of okra-leaf genetic traits for reducing colonization by B. tabaci. Results also suggest that okra-leaf shape may provide less favorable micro-environmental conditions for the habitat of B. tabaci because of more open canopy as evidenced by higher leaf perimeter to leaf area ratio. The okra-leaf cultivar 'Siokra L-23' appears to have genetic traits that should be examined further as a source of B. tabaci resistance.     

Efficacy of transgenic cotton containing a cry1Ac gene from Bacillus thuringiensis against Helicoverpa armigera (Lepidoptera: Noctuidae) in northern China

NuCOTN 33B, a Bt transgenic variety of upland cotton (Gossypium hirsutum L.) expressing the insecticidal protein Cry1Ac from Bacillus thuringiensis Berliner sp. kurstaki, was evaluated for resistance to Helicoverpa armigera (Hübner) during 1998-2000 in northern China. The results indicated that there was no significant difference in egg densities between NuCOTN 33B and three nontransgenic varieties (DP5415, Zhongmian12, and Shiyuan321) during the season, although the survival of larvae on NuCOTN 33B seemed significantly reduced. High larval densities observed on non-Bt cotton appeared in great contrast to the low larval populations observed on NuCOTN 33B plants during the seasons. In an environment without insecticide sprays, the annual ginned cotton yields in NuCOTN 33B plots, ranging from 1391.17 to 1511.35 kg/ha, were significantly higher than those in non-Bt cotton (340.34-359.58 kg/ha). These high levels of field efficacy for NuCOTN 33B against H. armigera in northern China may pave the way for reduced pesticide applications and an expansion of alternative pest-control strategies.     

Bollworm (Lepidoptera: Noctuidae) survival on 'Bollgard' and 'Bollgard II' cotton flower bud and flower components.

Genetically modified cotton, Gossypium hirsutum L., cultivars ('Bollgard') that produce crystalline proteins from Bacillus thuringiensis (Berliner) are valuable tools for managing lepidopteran insect pests in the United States. However, high numbers of bollworm, Helicoverpa zea (Boddie), larvae have been observed feeding in white flowers of these cultivars. Fresh tissue bioassays were conducted to investigate bollworm survival on Bollgard and 'Bollgard II' cottons. Bollworm survival was higher on square and flower anthers than on other floral structures on 'Deltapine 5415' (conventional cotton) and 'NuCOTN 33B' (Bollgard). Bollworm survival at 72 h was higher on all floral structures from Deltapine 5415 than on corresponding structures from NuCOTN 33B. ELISA tests indicated that CryIA(c) expression varied among plant parts; however, bollworm survival did not correlate with protein expression levels. Trends in bollworm survival on Bollgard II were similar to those on Bollgard and conventional cotton; however, survival was lower on all structures of Bollgard II than on corresponding structures of Bollgard and conventional cotton. These data support field observations of bollworm injury to white flowers and small bolls and provide a better understanding of larval behavior on Bollgard cotton.     

Effect of cotton cultivar on performance of Aphis gossypii (Homoptera: Aphididae) in Iran

Cotton aphids, Aphis gossypii Glover (Homoptera: Aphididae), obtained from cotton, Gossypium hirsutum L., fields in the Gorgan region of northern Iran, were colonized on 'Varamin' cotton plants in a growth chamber. The development, survivorship, and life table parameters of the cotton aphid were evaluated at 27.5 +/- 1 degrees C, 65 +/- 10% RH, and aphotoperiod of 14:10 (L:D) h of artificial light on five commonly growing cotton cultivars: Varamin, 'Sealand' (relatively resistant cultivar), 'Bakhtegan', 'Sahel' (both relatively susceptible cultivars), and 'Siokra' [resistant to Bemisia tabaci (Gennadius)]. The developmental times of immature stages ranged from 4.6 d on Bakhtegan and Varamin to 6.3 d on Sealand, whereas the immature survival was 97.5 to 65% on Sahel and Siokra, respectively. On average, there were 28.7, 28.3, 23.5, 20.1, and 16.8 nymphs produced per female on Sahel, Bakhtegan, Varamin, Sealand, and Siokra, respectively. The intrinsic rate of natural increase (r(m)) for cotton aphids on Sahel was the highest, whereas the values for r(m) varied from 0.284 (nymphs per female per d) on Siokra to 0.368 on Sahel. Jackknife estimates of generation times (T), net reproductive rate (R(0)), doubling time (DT), and finite rate of increase (lambda) on these cultivars were as follows: 9.79-10.84 d for T, 9.23-23.81 nymphs per female for R(0), 2.17-3.19 d for DT, and 1.28-1.38 nymphs per female per d for lambda. Cotton aphid performance was at its highest on Sahel and lowest on Siokra.     

Selection for higher yields and heat resistance in Pima cotton has caused genetically determined changes in stomatal conductances

Gas exchange analysis was used to characterize photosynthetic and stomatal responses to key environmental stimuli in five commercial lines of Pima cotton ( Gossypium barbadense L.) which represent a gradient of selection for higher yields and heat resistance, and a primitive, uncultivated G. barbadense. At constant light and vapor pressure deficit, stomatal conductance increased linearly with air temperature in the 23 to 36$C range in all five commercial lines, and conductance at each temperature increased as a function of selection. In contrast, photosynthetic rates had a low sensitivity to temperature in the 23 to 36$C range, particularly in the advanced lines. In a segregating F₂ population from a cross between the advanced line, Pima S-6, and the primitive cotton, B368, the slope of the stomatal response to temperature in each F₂ plant was positively correlated with the stomatal conductance measured at 40$C. An analysis of the frequency distribution of stomatal conductance in F₁ and F₂ progeny of the cross showed that the differences in stomatal conductance between lines were genetically determined. These data indicate that selection for higher yield and heat resistance in Pima cotton has caused genetically determined changes in stomatal properties. Characterization of the relationship between the altered stomatal properties and the attained increases in heat resistance and yields could make it possible to use these physiological traits as selection criteria in future breeding programs.     

Trade-offs among anti-herbivore resistance traits: insights from Gossypieae (Malvaceae)

Plant defense theories commonly predict negative correlations among anti-herbivore resistance traits. Although this prediction has been widely accepted, the majority of empirical studies have failed to account for similarities among species due to common ancestry, thus risking pseudoreplication. Wild cotton plants possess traits conferring both direct resistance (toxic leaf glands and trichomes) and indirect resistance (extrafloral nectaries that reward enemies of herbivores). The evidence for negative phenotypic correlations among these resistance traits was examined at two levels: within Gossypium thurberi (wild cotton) and across species in the cotton clade (Gossypieae). A phylogenetic analysis controlled for shared ancestry among species. Across the Gossypieae, a strong negative correlation emerged between the direct resistance traits, leaf gland and trichomes. This correlation may reflect costs of these traits, a negative genetic correlation, or redundancy in their actions against herbivores. In contrast, the direct resistance traits (glands and trichomes) were not correlated with the indirect resistance trait of extrafloral nectar, either within or across species. The robust lack of correlation suggests that these direct and indirect resistance mechanisms evolve independently over evolutionary time scales. This conclusion conflicts with both predictions of plant defense theory and the majority of prior comparisons of direct and indirect resistance traits and may reflect the facultative nature of indirect resistance in Gossypieae.     

Light interception and radiation use efficiency of okra and normal leaf cotton isolines

Okra-leaf cotton (Gossypium hirsutum L.) types have been reputed to produce equal or higher amounts of lint yield than normal-leaf types, while intercepting less or similar amounts of radiation. In this field study, okra- and normal-leaf cotton isolines were compared for their efficiency to produce dry matter utilizing intercepted radiation. At three weeks after first flower, the two leaf-shape isolines produced similar amounts of dry matter, with the okra-leaf type partitioning a larger fraction to fruiting organs. However, at the end of the season no differences in lint yield, yield components and fiber-quality properties were recorded between the two isolines. Fractional light interception throughout the period of the study was greater for the normal-leaf type compared to the okra-leaf type. The okra-leaf isoline utilized intercepted radiation more efficiently to produce dry matter. Values of radiation use efficiency were estimated at 1.897 and 2.636 g MJ⁻¹ of intercepted photosynthetically active radiation for the normal- and okra-leaf types, respectively. Growth chamber studies revealed similar single leaf carbon exchange rates, therefore radiation use efficiency differences between the leaf shape isolines could be attributed to light interception characteristics.     

Selecting for efficacy of Bollgard cotton cultivars against various Lepidoptera using forward breeding techniques

Studies during the past 5 yr have shown that the overall level of protein (Cry1Ac) produced from the cry1Ac transgene (Monsanto Co., St. Louis, MO) differ among commercial Bollgard cotton, Gossypium hirsutum L., cultivars. These differences between cultivars are under genetic control and have been correlated with efficacy of certain lepidopteran pests. Previous studies have shown that the parental background (i.e., non-Cry1Ac conventional cultivar) has a significant influence on the amount of Cry1Ac protein in Bollgard cultivars. Unlike the backcross technique commonly used to acquire commercial Bollgard cultivars, we used forward breeding to obtain cultivars of Bollgard cotton that were selected for various levels of Cry1Ac. These differences in the amount of Cry1Ac were correlated with growth and survival of two lepidopteran pests of cotton. Implications for effective resistance management as well as relative ease of this procedure are discussed.     

Genetic diversity and relationships of diploid and tetraploid cottons revealed using AFLP

Gossypium species (± 49) represent a vast resource of genetic diversity for the improvement of cultivated cotton. To determine intra- and inter-specific genetic relationships within a diverse collection of Gossypium taxa, we employed 16 AFLP primer combinations on three diploid species, Gossypium herbaceum L. (A1), Gossypium arboreum L. (A2) and Gossypium raimondii Ulbrich (D5), and 26 AD allotetraploid accessions (Gossypium barbadense L. and Gossypium hirsutum L.). A total of 1180 major AFLP bands were observed; 368 of these (31%) were polymorphic. Genetic similarities among all taxa ranged from 0.21 (between the diploid species G. arboreum and G. raimondii) up to 0.89 (within G. barbadense). Phenetic trees based on genetic similarities (UPGMA, N-J) were consistent with known taxonomic relationships. In some cases, well-supported phylogenetic relationships, as well as evidence of genetic reticulation, could also be inferred. UPGMA trees and principal coordinate analysis based on genetic similarity matrices were used to identify genetically distinct cultivars that are potentially important sources of germplasm for cotton improvement, particularly of fiber quality traits. We show that AFLP is useful for estimating genetic relationships across a wide range of taxonomic levels, and for analyzing the evolutionary and historical development of cotton cultivars at the genomic level. Received: 17 January 2000 / Accepted: 4 May 2000     

Effects of proportion and configuration of Bacillus thuringiensis cotton on pest abundance, damage, and yield

Bacillus thuringiensis (Bt) transgenic cotton, Gossypium hirsutum L., kills several economically important pests, reducing injury and increasing yields. Refuges of non-Bt cotton are currently planted with Bt cotton in different designs to slow pest resistance evolution. To compare the effects of differences in Bt/non-Bt plant heterogeneity found in different refuge designs on square (flower bud) damage, abscissions, sap-feeding herbivore densities, and yield in cotton, four types of 24-row cotton plots were planted in 2001 and 2002: 1) seed mixtures of Bt and non-Bt varieties, 2) 12-row strips of Bt and non-Bt, 3) solid Bt, and 4) solid non-Bt. For both years cotton bollworm, Helicoverpa zea (Boddie), damage was less in solid Bt plots than strips and mixtures and all were less than solid non-Bt plots. Cotton fleahopper, Pseudatomoscelis seriatus (Reuter), damage was affected by refuge, but only in 2002 when damage was greater in solid Bt plots than all other plots and greater in strips than solid non-Bt plots. Abscissions were least in solid non-Bt plots, and less in mixtures and strips than solid Bt plots. In 2001, western flower thrips, Frankliniella occidentalis (Pergande), density was greatest in mixtures, whereas sweetpotato whitefly, Bemisia tabaci (Gennadius), was greatest in solid Bt plots, and greater in mixtures than solid non-Bt plots. Yield also was affected by refuge, it was greater for solid Bt plots than for solid non-Bt plots and mixtures in 2001, but the reverse was true in 2002.     

Protein markers for identification of different species and varieties of cotton

Reference electrophoretic spectra that allow compiling electrophoretic formulas of certain cotton species and varieties were obtained on the basis of analysis of the electrophoretic spectrum of water-soluble and barely soluble proteins of seeds of diploid cotton species of genomic group A (Gossypium arboretum var. indicum, G. arboreum ssp. obtusifolum, G. herbaceum ssp. africanum, and G. herbaceum Harga), group C (G. australe, G. bickii, G. nelsone, and G. sturtianum), group D (G. davidsonii. G. harknessii. G. klotzschianum, G. raimondii, G. thurberi, and G. trilobum), and amphidiploid species of group AD (G. mustelinum, G. hirsutum ssp. palmeri, G. tricuspidatum Bagota, G. tricuspidatum Mari Galanta, G. barbadense L., and G. hirsutum L.).     

Kaolin particle film associated with increased cotton aphid infestations in cotton

Highly reflective white kaolin‐based particle film was sprayed on cotton, Gossypium hirsutum L. (Malvaceae), plots in south Texas during 2004 and 2005 to observe its effect on the cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae). Populations of cotton aphids on the ventral surfaces of leaves in the kaolin‐treated plots were greater than in non‐treated control plots during both years. Alate cotton aphids were attracted less to white than to other pan trap colors, and parasitism by Lysiphlebus spec. (Hymenoptera: Aphidiidae) was either unaffected or greater in the kaolin‐treated plots, hence these two factors (color and parasitism) do not explain the increased infestations in the treated plots. However, mean temperatures on the ventral surfaces of kaolin‐treated cotton leaves were cooler than those of control leaves. The observed temperature difference where cotton aphids reside on cotton leaves is a potential reason for the greater infestations in the kaolin treatment plots. Our study demonstrates that applications of kaolin can exacerbate a pest infestation in cotton.     

Inheritance of Resistance to Meloidoygne incognita in Primitive Cotton Accessions from Mexico

Few sources of resistance to root-knot nematodes (Meloidogyne incognita) in upland cotton (Gossypium hirsutum) have been utilized to develop resistant cultivars, making this resistance vulnerable to virulence in the pathogen population. The objectives of this study were to determine the inheritance of resistance in five primitive accessions of G. hirsutum (TX1174, TX1440, TX2076, TX2079, and TX2107) and to determine allelic relations with the genes for resistance in the genotypes Clevewilt-6 (CW) and Wild Mexico Jack Jones (WMJJ). A half-diallel experimental design was used to create 28 populations from crosses among these seven sources of resistance and the susceptible cultivar DeltaPine 90 (DP90). Resistance to M. incognita was measured as eggs per g roots in the parents, F(1) and F(2) generations of each cross. The resistance in CW and WMJJ was inherited as recessive traits, as reported previously for CW, whereas the resistance in the TX accessions was inherited as a dominant trait. Chi square analysis of segregation of resistance in the F(2) was used to estimate the numbers of genes that conditioned resistance. Resistance in CW and WMJJ appeared to be a multigenic trait whereas the resistance in the TX accessions best fit either a one or two gene model. The TX accessions were screened with nine SSR markers linked to resistance loci in other cotton genotypes. The TX accessions lacked the allele amplified by SSR marker CR316 and linked to resistance in CW and other resistant genotypes derived from this source. Four of five TX genotypes lacked the amplification products from the marker BNL1231 that is also associated with the resistant allele on Chromosome 11 in WMJJ, CW, NemX, M120 RNR and Auburn 634 RNR. However, all five TX genotypes produced the same amplification products from three SSR markers linked to the resistant allele on Chromosome 14 in M120 RNR and M240 RNR. The TX accessions have unique resistance genes that are likely to be useful in efforts to develop resistant cotton cultivars with increased durability.     

Phloem‐specific resistance in Brassica oleracea against the whitefly Aleyrodes proletella

The cabbage whitefly [Aleyrodes proletella L. (Hemiptera: Aleyrodidae)] is becoming a serious pest in Brassica oleracea L. (Brassicaceae) crops. However, almost nothing is known about the interaction of this insect with its host plants. Previous studies have shown differences in the natural occurrence of adults, eggs, and nymphs on the closely related B. oleracea cultivars Christmas Drumhead and Riviera grown in the field. In this study, we aimed to identify the nature of these differences and to gain insight into the resistance mechanisms against A. proletella. We used no‐choice experiments on field‐ and greenhouse‐grown plants to show that the differences between the two cultivars are mainly based on antibiosis (traits that reduce herbivore performance) and not on antixenosis (traits that deter herbivory). This was further supported by laboratory choice experiments that indicated little or no discrimination between the two cultivars based on plant volatiles. We showed that resistance is dependent on plant age, that is, resistance increased during plant development, and is mainly independent of environmental factors. Analysis of probing behaviour revealed that the resistance trait affects A. proletella at the phloem level and that morphological differences between the two cultivars are most likely not involved. We suggest that compounds present in the phloem reduce sap ingestion by the whitefly and that this explains the observed resistance.     

Quantifying Potential Tolerance of Selected Cotton Cultivars to Belonolaimus longicaudatus

Glyphosate-tolerant cotton cultivars were evaluated for tolerance to Belonolaimus longicaudatus in field experiments conducted from 2004 to 2005. Field trials were arranged in a split-plot design that included treatment with four levels of 1, 3-dichloropropene (0.0, 13.9, 27.8, and 41.7 1 a.i./ha) to establish a range of population densities of B. longicaudatus. Six cotton cultivars (early-to-mid maturity: DP444BG/RR SG501BR, ST5242BR; mid-to late maturity: DP451B/RR, ST5599BR, DP655BRR) were planted as whole plots. Fumigation was effective in suppressing B. longicaudatus population densities at mid-season, but not at cotton harvest, and increased cotton lint yield. The cultivar × fumigation interaction for cotton lint yield was not significant for the six cultivars evaluated, indicating that tolerance did not occur in this nematode-host combination. Early-to-mid maturity cultivars yielded significantly more than mid-to-late maturity cultivars in both years. Small but significant differences in nematode final population density were observed between cultivars that may be related to relative maturity.     

Effect of cotton nitrogen fertilization on Bemisia argentifolii populations and honeydew production

The impact of nitrogen fertilization on cotton plants, Gossypium hirsutum L., silverleaf whitefly, Bemisia argentifolii Bellows & Perring, population dynamics and honeydew production were investigated in the field at Riverside, California, USA. Treatments were soil applications of 0, 112, 168 and 224 kg nitrogen per hectare, and a soil application of 112 kg of nitrogen plus a foliar application of 17 kg nitrogen per hectare. Increased numbers of both adult and immature whiteflies occurred during population peaks with increasing amounts of applied nitrogen. Higher numbers of whiteflies resulted in increased levels of honeydew. Increasing plant nitrogen also enhanced cotton foliar photosynthetic rates and stomatal conductance, and altered concentrations of glucose, fructose and sucrose in cotton petioles. However, at our treatment levels nitrogen had no effect on seedcotton yield. Petiole glucose levels were significantly correlated with numbers of whitefly adults on leaves during their peak populations. Significant correlations between whitefly numbers and other cotton physiological parameters occurred on only a few sampling dates.     

Effect of planting date and nitrogen fertilization on photosynthesis and soluble carbohydrate contents of cotton in relation to silverleaf whitefly （Bemisia tabaci biotype “B”） populations

The impacts of planting date and nitrogen fertilization on cotton （Gossypium hirsutum L.） photosynthesis and soluble carbohydrate contents in relation to silverleaf whitefly, Bemisia tabaci （Gennadius） biotype “B”, populations were examined in field experiments. Cotton planted in late April and early June was treated with 0, 112, 168 and 224 kg/N hectare in soil using urea fertilizer. The mean photosynthetic rate of April-planted cotton was 4%-20% higher than that of June-planted cotton early in the season, but 10%- 18% lower than that of June-planted cotton late in the season. The photosynthetic rates for both planting dates were positively correlated with levels of added nitrogen. While levels of glucose for both planting dates were positively correlated with nitrogen levels, fructose and sucrose levels were not. The mean levels of fructose were up to 40% lower, while that of sucrose were up to 59% higher, in April-planted cotton than in June-planted cotton. Levels of photosynthetic rate or stomatal conductance were not correlated with adult whitefly densities for either planting date. Levels of glucose and fructose were positively correlated with whitefly densities only for June-planted cotton late in the season.     

Lack of fitness costs associated with acetamiprid resistance in Bemisia tabaci (Hemiptera: Aleyrodidae)

Sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is a devastating pest that can cause severe damage to a range of crops by direct feeding and by plant virus transmission. Because of indiscriminate use of insecticides, this whitefly has developed resistance to several insecticides, including neonicotinoids. Our objectives were to determine fitness components affected by acetamiprid resistance in B. tabaci. Assay results showed that selection with acetamiprid had removed heterozygotes from the field population because the survival rate of the resistant population was significantly greater than that of the field population at a very high dose. Comparison of various life traits between the acetamiprid-selected (Aceta-SEL) population and three other populations showed that the numbers of eggs laid by acetamiprid Aceta-SEL population were significantly lower compared with that of other populations but that the proportions of eggs hatched were significantly higher. However, the time taken by nymphal stages of the Aceta-SEL population to develop was significantly higher than that of the susceptible populations. The intrinsic rate of increase, net reproductive rate, mean generation time, and doubling time of Aceta-SEL was significantly higher than Lab-PK and UNSEL populations, but the growth index was similar for all populations. The growth index and high intrinsic value of Aceta-SEL population suggest that the resistance allele may not have detrimental impact. The lack of fitness costs in B. tabaci could promote the rapid development of resistance to acetamiprid and other neonicotinoids. This resistance could threaten the sustainability of whitefly management program on genetically engineered cotton (Gossypium hirsutum L.) where neonicotinoids are being sprayed to manage sucking pests in the field.