Mapping quantitative trait loci associated with leaf and stem pubescence in cotton

Leaf pubescence in cotton have a potential for insect pest management. Varying degrees of leaf trichome density in Gossypium species and cultivars have been associated to a series of five genes, referred to as t(1)-t(5). We used two segregating interspecific G. hirsutum x G. barbadense backcross populations developed in our laboratory to assess qualitatively and quantitatively leaf and stem pubescence. QTL analyses were performed using simple and composite interval mapping. Based on both types of measurements and under both types of QTL analyses, nine QTLs met permutation-based thresholds. The nine QTLs mapped to four different chromosome regions. Highest LOD values corresponded to the QTLs detected on c6 (four colocalized QTLs) and on D03 (two QTLs) for which the higher pubescence in the progeny derived from the pubescent G. hirsutum parent alleles. Conversely, on c17 (one QTL) and A01 (two QTLs), the G. hirsutum parental alleles affected negatively pubescence. These results combined with another published study confirm (1) the location in a center region of chromosome 6 of the t(1) locus as a major locus/gene determining leaf pubescence, and (2) additional genes located on seven additional chromosomes have been shown to impart trichome density either positively or negatively. The existence of a high density of PCR-based loci in most of the regions identified as harboring leaf pubescence QTLs, particularly that on chromosome 6, will facilitate future efforts for map-based cloning.     

Interaction of bean leaf pubescence with rust urediniospore deposition and subsequent infection density

The role of dense straight trichomes on bean leaves associated with race-nonspecific resistance to rust was studied using a settling tower method for uniform inoculation. Abaxial leaf trichomes, which occur only on adult leaves, trapped significant numbers of urediniospores, especially those deposited in clusters, and resulted in reduced effective inoculum reaching the leaf surface. In the field where infection conditions are often less than optimum, leaf pubescence would partially explain the observed resistance. However, the observed increase in total number of spores as well as similar infection densities on fully expanded leaves of glabrous and pubescent genotypes cannot be explained by the trichomes. Other physical or chemical features of the leaf surface such as waxes or cations may play a role. The ecological fit of leaf pubescence is discussed.     

Soybean leaf pubescence affects aphid vector transmission and field spread of soybean mosaic virus

A study was undertaken to determine the influence of trichome density on the spread of non-persistently transmitted plant viruses by aphid vectors. A system using soybean plants and soybean mosaic virus (SMV) tested the hypothesis that greater leaf trichome density inhibits probing activity of vector species, leading to reduced virus spread and retarded virus epidemics under field conditions. Probing activity of three important aphid vectors of SMV, Myzus persicae, Rhopalosiphum maidis, and Aphis citricola, was affected by the density of soybean leaf trichomes. Less pubescent and glabrous isolines elicited greater probing activity than did densely pubescent isolines. Among the parameters considered, probe duration was found to be species specific, whereas the following traits were consistent among species for the denser isolines: reduced numbers of probes, greater length of time to first probe, and less time spent probing. Laboratory transmission of soybean mosaic virus was reduced in the more densely pubescent isolines by the vector species tested. Field spread of SMV was negatively correlated with density of pubescence. In our system, we found that denser leaf pubescence retards field epidemics of non-persistently transmitted plant viruses.     

Leaf pubescence mediates intraguild predation between predatory mites

Plant morphological traits such as leaf pubescence may affect herbivores and their natural enemies at the individual, population and community levels. Leaf pubescence has been repeatedly shown to mediate predator‐herbivore interactions whereas the influence of leaf pubescence on predator–predator interactions such as intraguild predation (IGP) has seldom been investigated. Using a three‐pronged approach we assessed the influence of leaf pubescence on the predatory mites Kampimodromus aberrans and Euseius finlandicus. Both predators occur on broad‐leaved trees in Europe. Euseius finlandicus is mostly found on trees with glabrous leaves whereas K. aberrans mainly occurs on trees with pubescent leaves. We hypothesized that leaf pubescence mediates IGP between K. aberrans and E. finlandicus and thereby determines their dominance and proportional abundance. A field survey on apple revealed that the abundance of K. aberrans and E. finlandicus is negatively correlated, with the former predominating on cultivars with strongly pubescent leaves and the latter predominating on cultivars with little pubescent or glabrous leaves. Microhabitat choice tests showed that K. aberrans preferentially resides on pubescent leaves whereas E. finlandicus preferentially resides on glabrous leaves. The effects of leaf pubescence on survival and development of immature IG predators and IG prey were reversed for K. aberrans and E. finlandicus. In the presence of the IG predator E. finlandicus, immature K. aberrans had higher survival probabilities on pubescent leaves than on glabrous ones. In contrast, the survival chances of immature E. finlandicus were higher on glabrous leaves than on pubescent ones when the IG predator K. aberrans was present. Artificial leaf pubescence enhanced IG prey capture by immature K. aberrans and prolonged their longevity but impaired IG prey capture by immature E. finlandicus and shortened their longevity. We conclude that leaf pubescence mediates IGP strength and symmetry and discuss the implications to natural and biological control.     

PATTERNS OF VARIATION IN FOLIAR TRICHOMES OF EASTERN NORTH AMERICAN QUERCUS

Scanning electron microscopy of leaf trichomes of the forty two native species of oaks in eastern North America indicates five patterns of variability: 1) Eight trichome types are evident among the species and each species possesses a definite complement of trichome types. Certain trichomes are restricted to particular subgenera and series. 2) An obvious seasonal loss of trichomes occurs during leaf maturation. This loss may be both quantitative in terms of trichome density and qualitative in terms of trichome type. 3) There is an obvious difference between the adaxial and abaxial surfaces. The adaxial side of most oak leaves is dark green, lustrous, and glabrous or glabrate. The abaxial surface either remains pubescent, becomes glabrate or glabrous, or maintains trichomes along the midrib or in the axils of major secondary veins. There are also initial quantitative and qualitative trichome differences between the two sides. 4) Geographical and ecological variations are due in part to non-genetic ecophenic modifications, ecotypic differentiation, and random genetic differences not necessarily correlated with environmental conditions. Trichome types are considered to be less affected by environment than is trichome density. 5) Hybridization and introgression within a subgenus leads to localized variability. Trichomes of hybrids are usually a combination of the parental types. These five patterns of variation are predictable and appear to be held within rather narrow limits. The complement of foliar trichomes, therefore, is a reliable character in the taxonomy of the oaks.     

Effect of trichome density on soybean pod feeding by adult bean leaf beetles (Coleoptera: Chrysomelidae).

The role of soybean, Glycine max (L.) Merrill, pod trichomes on feeding by adult bean leaf beetles. Cerotoma trifurcata (Forster), was evaluated under laboratory and field conditions during 1997 and 1998. Three Clark isolines and 'Corsoy 79' were used to compare the feeding preference of the beetle on pods with different trichome densities. The three Clark isolines, including densely pubescent, sparsely pubescent, and glabrous, were isogenic except for trichome density. The trichome densities on the pods of Clark densely pubescent, Clark sparsely pubescent, and Corsoy 79 were significantly different. In no-choice tests, under both laboratory and field conditions, the feeding on pods of Clark densely pubescent was significantly lower than that on the other isolines. In the choice test of Corsoy 79 conducted in the laboratory and field, when the trichomes on one of the two pods were shaven off, the feeding on the shaven pods was significantly higher than that of the intact ones. In the choice test among Clark isolines under laboratory condition, the result was significant, with the lowest feeding on the densely pubescent pods. This study demonstrates that densely pubescent soybean has the potential to resist bean leaf beetle feeding on pods.     

QTL mapping in A-genome diploid Asiatic cotton and their congruence analysis with AD-genome tetraploid cotton in genus Gossypium

Asiatic cotton(Gossypium arboreum L.) is an Old World cultivated cotton species.The sinense race was planted extensively in China.Due to the advances in spinning technology during the last century,the species was replaced by the New World allotetraploid cotton G.hirsutum L.Gossypium arboreum is still grown in India and Pakistan and also used as an elite in current cotton breeding programs.In addition,G.arboreum serves as a model for genomic research in Gossypium.In the present study,we generated an A-genome diploid cotton intraspecific genetic map including 264 SSR loci with three morphological markers mapped to 1 3 linkage groups.The map spans 2,508.71 cM with an average distance of 9.4 cM between adjacent loci.A population containing 1 76 F2:3 families was used to perform quantitative trait loci(QTL)mapping for 17 phenotypes using Multiple QTL Model(MQM)of MapQTL ver 5.0.Overall,108 QTLs were detected on 13 chromosomes.Thirty-one QTLs for yield and its components were detected in the F2 population.Forty-one QTLs for yield and its components were detected in the F2:3 families with a total of 43 QTLs for fiber qualities.Two QTLs for seed cotton weight/plant and lint index and three QTLs for seed index were consistently detected both in F2 and F2:3.Most QTLs for fiber qualities and yields were located at the same interval or neighboring intervals.These results indicated that the negative correlation between fiber qualities and yield traits may result from either pleiotropic effect of one gene or linkage effects of multiple closely linked genes.     

Effects of leaf pubescence in Salix borealis on host- plant choice and feeding behaviour of the leaf beetle, Melasoma lapponica

Density of leaf trichomes in Salix borealis affected both the choice of individual host plants and feeding behaviour of adults and last instar larvae of the willow feeding leaf beetle, Melasoma lapponica. Beetles clearly preferred shaved disks to unshaved ones taken from the same leaf; this preference was highest in leaves of the most pubescent plants. High leaf pubescence explained the low preference for willow clones from the high density site in among-site preference trials; shaving significantly increased the consumption of these pubescent willow clones. In no-choice experiments, the food consumption by both adults and last instar larvae decreased with an increase in leaf pubescence. The time budget of adults did not depend on leaf pubescence of the host plants, however adults compelled to feed on highly pubescent plants changed their feeding sites twice as often as on less pubescent willow clones. Larvae feeding on highly pubescent plants spend moving three times as much time as larvae feeding on less pubescent plants. Combined with our earlier observations on the increase in leaf pubescence in the year(s) following defoliation, these data suggest that leaf hairiness may have contributed to the delayed induced resistance in S. borealis by disturbing the feeding behaviour of M. lapponica.     

Modelled influences of non-exchanging trichomes on leaf boundary layers and gas exchange

The two main resistances in the exchange of gases between plants and the atmosphere are stomatal and boundary layer resistances. We modeled boundary layer dynamics over glabrous and pubescent leaves (assuming non-exchanging trichomes) with leaf lengths varying from 0.01 to 0.2 m, and windspeeds of 0.1-5.0 m x s(-1). Results from theoretical and semi-empirical formulae were compared. As expected, boundary layer thickness decreased with decreasing leaf length and increasing windspeed. The presence of trichomes increased leaf surface roughness, resulting in lowered Reynolds numbers at which the boundary layer became turbulent. This effect is especially important at low windspeeds and over small leaves, where the Reynolds number over glabrous surfaces would be low. We derived a new simple dimensionless number, the trip factor, to distinguish field conditions that would lead to a turbulent boundary layer based on the influence of trichomes. Because modeled rates of CO2 and H2O(v) exchange over turbulent boundary layers are one or more orders of magnitude faster than over laminar boundary layers, a turbulent boundary layer may lead to increased carbon uptake by plants. The biological trade-off is potentially increased transpirational water loss. However, in understory habitats characterized by low windspeeds, even a few trichomes may increase turbulence in the boundary layer, thus facilitating photosynthetic gas exchange. Preliminary field data show that critical trip factors are exceeded for several plant species, both in understory and open habitats.     

Trichomes and spider-mite webbing protect predatory mite eggs from intraguild predation

Predaceous arthropods are frequently more abundant on plants with leaves that are pubescent or bear domatia than on plants with glabrous leaves. We explored the hypothesis that for some predatory mites this is because pubescence affords protection from intraguild predation. In laboratory experiments, we tested whether apple leaf pubescence protected Typhlodromus pyri eggs from predation by western flower thrips, Frankliniella occidentalis. To investigate the effect of pubescence further, we added cotton fibers to trichome-free leaves. We also determined whether webbing produced by Tetranychus urticae protected Phytoseiulus persimilis eggs from predation by F. occidentalis. Predation by thrips on T. pyri eggs oviposited on field-collected pubescent "Erwin Bauer" apple leaves was significantly less than on glabrous "Crittenden" apple leaves. Phytoseiid eggs oviposited in the cotton fibers were preyed upon significantly less than those on the trichome-free bean disk. Increasing the cotton fiber density from 5 to 20 fibers only slightly further reduced predation by thrips on T. pyri eggs. Thrips fed upon significantly fewer P. persimilis eggs oviposited in Te. urticae webbing than eggs oviposited on a surface that differed only in the absence of Te. urticae web. We conclude that a complex leaf topography reduces intensity of intraguild predation in this system.     

6-Benzylaminopurine treatment induces increased pubescence on wheat leaves

The epidermis of wheat (Triticum aestivum L.) leaves contains trichomes that contribute to resistance to insect pests and drought tolerance. In the present study, we examined the effects of 6-benzylaminopurine (BA) and methyl jasmonate (MeJA) treatment on trichome development on the leaves of wheat cv. Norin 61 seedlings. Without phytohormone treatment, trichomes on the adaxial leaf surface were short (90 μm) and their density was low (3.6 trichomes/mm²). Both BA and MeJA treatments significantly increased the density of trichomes, and there were no significant differences between the phytohormone treatments. BA treatment increased trichome length to five times as long as that in the control, whereas MeJA treatment did not significantly affect trichome length. Since BA treatment concurrently increased the DNA content of the nuclei in trichome cells, endoreduplication of the nuclei is probably involved in trichome enlargement. These results indicate that even wheat cultivars with short trichomes retain the mechanisms for trichome enlargement and stimuli such as BA application can induce increased pubescence on wheat leaves.     

RFLP-facilitated investigation of the quantitative resistance of rice to brown planthopper ( Nilaparvata lugens)

Quantitative trait loci (QTLs), conferring quantitative resistance to rice brown planthopper (BPH), were investigated using 160 F₁₁ recombinant inbred lines (RILs) from the Lemont/Teqing cross, a complete RFLP map, and replicated phenotyping of seedbox inoculation. The paternal indica parent, Teqing, was more-resistant to BPH than the maternal japonica parent, Lemont. The RILs showed transgressive segregation for resistance to BPH. Seven main-effect QTLs and many epistatic QTL pairs were identified and mapped on the 12 rice chromosomes. Collectively, the main-effect and epistatic QTLs accounted for over 70% of the total variation in damage scores. Teqing has the resistance allele at four main-effect QTLs, and the Lemont allele resulted in resistance at the other three. Of the main-effect QTLs identified, QBphr5b was mapped to the vicinity of gl1, a major gene controlling leaf and stem pubescence. The Teqing allele controlling leaf and stem pubescence was associated with resistance, while the Lemont allele for glabrous stem and leaves was associated with susceptibility, indicating that this gene may have contributed to resistance through antixenosis. Similar to the reported BPH resistance genes, the other six detected main-effect QTLs were all mapped to regions where major disease resistance genes locate, suggesting they might have contributed either to antibiosis or tolerance. Our results indicated that marker-aided pyramiding of major resistance genes and QTLs should provide effective and stable control over this devastating pest. Received: 10 December 2000 / Accepted: 7 May 2001     

Contrasting Structure and Function of Pubescent and Glabrous Varieties of Hawaiian Metrosideros polymorpha (Myrtaceae) at High Elevation

Hawaiian dominant tree species Metrosideros polymorpha varieties glaberrima and polymorpha have glabrous and pubescent leaves, respectively. Sympatric populations at 2040 m elevation showed major differentiation beyond the pubescence itself. The varieties differed substantially in stomatal traits and in leaf composition, leaf water status, and instantaneous gas exchange rates, despite similarity in leaf and wood cross-sectional anatomy. Functional differentiation among varieties represents a possible mechanism facilitating the occupation of an exceptional ecological range.     

Chromosome structural changes in diploid and tetraploid A genomes of Gossypium.

The genus Gossypium, which comprises a divergent group of diploid species and several recently formed allotetraploids, offers an excellent opportunity to study polyploid genome evolution. In this study, chromosome structural variation among the A, At, and D genomes of Gossypium was evaluated by comparative genetic linkage mapping. We constructed a fully resolved RFLP linkage map for the diploid A genome consisting of 275 loci using an F2 interspecific Gossypium arboreum x Gossypium herbaceum family. The 13 chromosomes of the A genome are represented by 12 large linkage groups in our map, reflecting an expected interchromosomal translocation between G. arboreum and G. herbaceum. The A-genome chromosomes are largely collinear with the D genomes, save for a few small inversions. Although the 2 diploid mapping parents represent the closest living relatives of the allotetraploid At-genome progenitor, 2 translocations and 7 inversions were observed between the A and At genomes. The recombination rates are similar between the 2 diploid genomes; however, the At genome shows a 93% increase in recombination relative to its diploid progenitors. Elevated recombination in the Dt genome was reported previously. These data on the At genome thus indicate that elevated recombination was a general property of allotetraploidy in cotton.     

关于棉属四倍体种起源问题的过氧化物酶同工酶研究

本文采用聚丙烯酰胺凝胶垂直板电泳和等电聚焦技术,对棉属(Gossypium)A基因组2个二倍体种、D基因组10个二倍体野生种和四倍体2(AD)基因组的3个种进行过氧化物酶同工酶酶谱分析。种间酶谱关系符合形态学,细胞学和遗传学的研究结果,但G.gossypioides,G.thurberi和G.trilobum的酶谱与D基因组其他种有较大差异却与A基因组相似。由二倍体种酶液组成的体外人工混合体与自然四倍体的比较分析表明,四倍体棉种G.darwinii,G.barbadense和G.hirsutum是A基因组和D基因组的异质组合,G.raimondii而不是G.thurberi或G.trilobum为四倍体种祖先基因组的最可能的D亚基因组供体。对过氧化物酶同工酶分析为棉属种间亲缘关系和四倍体起源的研究提供生化遗传依据的可行性进行了阐述。     

Differential regulation of trichome formation on the adaxial and abaxial leaf surfaces by gibberellins and photoperiod in Arabidopsis thaliana (L.) Heynh.

In wild-type (WT) Columbia and Landsberg erecta ecotypes of Arabidopsis thaliana (L.) Heynh., trichomes are present on the adaxial surfaces of all rosette leaves but are absent from the abaxial surfaces of the first-formed leaves. We have determined that both long-day (LD) photoperiod and gibberellin (GA) stimulate trichome formation. WT plants grown in LD conditions produce the first abaxial trichome on earlier leaves than plants grown in short-day (SD) conditions. Photoperiod sensitivity of abaxial trichome formation on WT plants develops gradually over time, reaching the maximum sensitivity about 24 d after germination. Application of gibberellic acid to WT plants growing in SD conditions accelerates the onset of abaxial trichomes. Conversely, application of 20 to 80 mg L-1 paclobutrazol, a GA biosynthesis inhibitor, to wild-type plants suppresses trichome initiation on the abaxial epidermis. The GA-deficient mutants ga1-5 and ga4-1 and the GA-insensitive mutant gai-1 exhibit delayed onset of abaxial trichomes when grown in LD conditions. The null mutant ga1-3 produces completely glabrous leaves when grown in SD conditions. Application of gibberellic acid to glabrous ga1-3 plants consistently induces earlier formation of trichomes on the adaxial epidermis than on the abaxial epidermis, demonstrating a difference between the adaxial and abaxial surfaces in their response to GA with regard to trichome formation.     

Incidence of the introduced parasitoids Cotesia kazak and Microplitis croceipes (Hymenoptera: Braconidae) from Helicoverpa armigera (Lepidoptera: Noctuidae) in tomatoes, sweet corn, and lucerne in New Zealand

Morphological defense traits of plants such as trichomes potentially compromise biological control in agroecosystems because they may hinder predation by natural enemies. To investigate whether plant trichomes hinder red imported fire ants, Solenopsis invicta Buren (Hymenoptera: Formicidae), as biological control agents in soybean, field and greenhouse experiments were conducted in which we manipulated fire ant density in plots of three soybean isolines varying in trichome density. Resulting treatment effects on the abundance of herbivores, other natural enemies, plant herbivory, and yield were assessed. Trichomes did not inhibit fire ants from foraging on plants in the field or in the greenhouse, and fire ant predation of herbivores in the field was actually greater on pubescent plants relative to glabrous plants. Consequently, fire ants more strongly reduced plant damage by herbivores on pubescent plants. This effect, however, did not translate into greater yield from pubescent plants at high fire ant densities. Intraguild predation by fire ants, in contrast, was weak, inconsistent, and did not vary with trichome density. Rather than hindering fire ant predation, therefore, soybean trichomes instead increased fire ant predation of herbivores resulting in enhanced tritrophic effects of fire ants on pubescent plants. This effect was likely the result of a functional response by fire ants to the greater abundance of caterpillar prey on pubescent plants. Given the ubiquity of lepidopteran herbivores and the functional response to prey shown by many generalist arthropod predators, a positive indirect effect of trichomes on predation by natural enemies might be more far more common than is currently appreciated.