In recent years, the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae), has become the most destructive insect of cruciferous plants throughout the world, and the annual cost for managing it is estimated to be US $I billion (168) Members of the plant family Cruciferae occur temperate and tropical climates and represent a diverse, widespread, and important plant group that includes cabbage, broccoli, cauliflower, collards, rapeseed, mustard, and Chinese cabbage, the most important vegetable crop grown in China (90), the most populous country in the world Although the diamondback moth is believed to have originated in the Mediterranean area (64), the source of some of our most important crucifers (185), diamondback moths now occur wherever cmcifers are grown, and this insect is believed to be the most universally distributed of all Lepidoptera (107) Absence of effective natural enemies, especially parasitoids, is believed to be a major cause of the diamondback moth’s pest status in most parts of the world (92) Lack of parasitoids in a particular area may have occurred because the diamondback moth is better able than its natural-enemy complex to become established in newly planted cmcifers Reports on the ability of diamondback moths to migrate long distances are numerous (19, 40, 54, 58, 108, 120,

http://web.entomology.cornell.edu/shelton/publications/pdf/Talekar-Shelton_1993_Ann_Rev_Ent_DBM.pdf

Biology, Ecology, and Management of the Diamondback Moth

A unified presentation, a synthesis, and an evaluation of the methods employed in the estimation of heritability in plants are presented. Asexual, cross‐fertilizing, and self‐fertilizing diploid species, as well as annual and perennial ones, are considered. All broad‐ and narrow‐sense heritabilities are defined on individual and family bases for prediction of response to selection for a target population of environments in space and time. Narrow‐sense heritabilities are defined in cross‐fertilizing species for expected response to variations of mass, half‐sib, and full‐sib family selection for the next generation and the long term, and similarly in self‐fertilizing species. The use of both collateral and lineal relatives to estimate heritability is discussed, and the biases present in the estimators are given. Many departures and variations of the common procedures are discussed. The standard errors of heritability estimators and confidence intervals are presented.

Estimation of heritability and prediction of selection response in plant populations

The primary role of epicuticular lipids on aerial plant surfaces is prevention of water loss, but their species-specific chemical composition and their vari­ able crystal morphology suggest other ecological functions. Among these functions is mediation of interactions between plants and insect herbivores. Epicuticular lipid extracts and individual lipid components enhance or deter oviposition, movement, and feeding. The physical structure of plant surface lipids can affect insect herbivore attachment and locomotion. Surface lipids may also affect herbivores indirectly by influencing predatory and parasitic insects. Glossy crop phenotypes are often less susceptible to insect herbivores than are normal phenotypes. The epicuticular lipids of glossy plants are usually reduced in amount and have dramatically different chemical compo­ sition and morphology. Study of the basis of the reduced suscept ibility of glossy plants can help elucidate the role of plant surface lipids in insect-plant interactions.

Effects of Plant Epicuticular Lipids on Insect Herbivores

Neonate Lepidoptera are confronted with the daunting task of establishing themselves on a food plant. The factors relevant to this process need to be considered at spatial and temporal scales relevant to the larva and not the investigator. Neonates have to cope with an array of plant surface characters as well as internal characters once the integument is ruptured. These characters, as well as microclimatic conditions, vary within and between plant modules and interact with larval feeding requirements, strongly affecting movement behavior, which may be extensive even for such small organisms. In addition to these factors, there is an array of predators, pathogens, and parasitoids with which first instars must contend. Not surprisingly, mortality in neonates is high but can vary widely. Experimental and manipulative studies, as well as detailed observations of the animal, are vital if the subtle interaction of factors responsible for this high and variable mortality are to be understood. These studies are essential for an understanding of theories linking female oviposition behavior with larval survival, plant defense theory, and population dynamics, as well as modern crop resistance breeding programs.

Ecology and behavior of first instar larval lepidoptera

Background
Xanthomonas campestris pv. campestris (Xcc) (Pammel) Dowson is a Gram-negative bacterium that causes black rot, the most important disease of vegetable brassica crops worldwide. Intensive molecular investigation of Xcc is gaining momentum and several whole genome sequences are available.

Taxonomy
Bacteria; Phylum Proteobacteria; Class Gammaproteobacteria; Order Xanthomonadales; Family Xanthomonadacea; Genus Xanthomonas; Species X. campestris.

Host range and symptoms
Xcc can cause disease in a large number of species of Brassicaceae (ex-Cruciferae), including economically important vegetable Brassica crops and a number of other cruciferous crops, ornamentals and weeds, including the model plant Arabidopsis thaliana. Black rot is a systemic vascular disease. Typical disease symptoms include V-shaped yellow lesions starting from the leaf margins and blackening of the veins.

Race structure, pathogenesis and epidemiology
Collections of Xcc isolates have been differentiated into physiological races based on the response of several brassica species lines. Black rot is a seed-borne disease. The disease is favoured by warm, humid conditions and can spread rapidly from rain dispersal and irrigation water.

Disease control
The control of black rot is difficult and relies on the use of pathogen-free planting material and the elimination of other potential inoculum sources (infected crop debris and cruciferous weeds). Major gene resistance is very rare in B. oleracea (brassica C genome). Resistance is more readily available in other species, including potentially useful sources of broad-spectrum resistance in B. rapa and B. carinata (A and BC genomes, respectively) and in the wild relative A. thaliana.

Genome
The reference genomes of three isolates have been released. The genome consists of a single chromosome of approximately 5 100 000 bp, with a GC content of approximately 65% and an average predicted number of coding DNA sequences (CDS) of 4308.

Important genes identified
Three different secretion systems have been identified and studied in Xcc. The gene clusters xps and xcs encode a type II secretion system and xps genes have been linked to pathogenicity. The role of the type IV secretion system in pathogenicity is still uncertain. The hrp gene cluster encodes a type III secretion system that is associated with pathogenicity. An inventory of candidate effector genes has been assembled based on homology with known effectors. A range of other genes have been associated with virulence and pathogenicity, including the rpf, gum and wxc genes involved in the regulation of the synthesis of extracellular degrading enzymes, xanthan gum and lipopolysaccharides.

Xanthomonas campestris pv. campestris (cause of black rot of crucifers) in the genomic era is still a worldwide threat to brassica crops

For Brassica crop breeders, weedy crucifers are potential sources of disease resistance and other useful traits. However, few species have been evaluated or are well represented in germplasm collections. In this study, we evaluated 24 Eurasian crucifer species for disease reaction to North American isolates of the crop pathogens A. brassicicola and X. campestris pv. campestris. The test array comprised 190 entries (genebank accessions and weed populations), including 108 B. nigra entries from four geographic regions and 34 entries of Camelina sativa. Disease reaction was highly variable between species and within some species. Reaction to A. brassicicola was variable between entries of C. sativa, a species reported as highly resistant to Alternaria pathogens. In B. nigra, disease reaction was variable between geographic regions and between entries within some regions. Most of the B. nigra entries rated as disease resistant were weed populations from North America, but disease reaction was not related to the geographic distance between these populations. In summary, disease reaction to two crop pathogens was variable in crucifer weed taxa, including species considered to contain little genetic variation. We identified entries with promising levels of disease resistance and highlighted the potential value of weedy crucifer genetic resources.

Regional variation in Brassica nigra and other weedy crucifers for disease reaction to Alternaria brassicicola and Xanthomonas campestris pv. campestris

Survival of larvae of the diamondback moth, Plutella xylostella (L.) was reduced on several genotypes of cabbage from the breeding program at Geneva, N.Y. Polar fractions of ethanol extracts of partially resistant lines 2535 and 2503, when incorporated into diet, reduced survival of P. xylostella larvae by 14.9 and 19.0%, respectively. Whether this effect was due to reduced feeding or postingestive toxicity was not determined. Although survival on glossy-leafed line 2518 was very low in the field and larvae on this line failed to form visible feeding mines during the first 72 h after egg hatch, extracts from 2518 had no activity. Survival of larvae confined on leaf disks of 2518 in the laboratory was much greater (80% of controls) than it was on whole plants in the field (0.36% of controls). In the field, neonate P. xylostella dispersed two to three times more rapidly on the leaves of 2518 than on other lines. Resistance to P. xylostella in the lines investigated was therefore due to at least two mechanisms, (1) antibiosis or nonpreference due to extractable compounds present in normal bloom resistant cabbage genotypes, 2503 and 2535, and (2) possible nonpreference for glossy-leafed 2518 by neonate larvae, as suggested by the greater dispersal rates of neonates on these plants. Survival is relatively high on 2518 in leaf disk bioassays in the laboratory, suggesting that nonpreference in combination with environmental stresses to larvae in the field may produce P. xylostella resistance in the glossy 2518.

/pdf/two-types-of-resistance-to-the-diamondback-moth-lepidoptera-25m4cl2pir.pdf

Two Types of Resistance to the Diamondback Moth (Lepidoptera: Plutellidae) in Cabbage

Differences in susceptibility to damage by Thrips tabaci Lindeman and the lepidopteran pest complex (Plutella xylostella (L.), Artogeia rapae (L.), and Trichoplusia ni (Hubner)) were documented and analyzed for fresh market and experimental cabbage varieties. Patterns of resistance to damage were different for Lepidoptera and T. tabaci . The commercial green varieties did not differ in susceptibility to damage by Lepidoptera but did differ in susceptibility to damage by T. tabaci . The two experimental varieties and one commercial red variety, used for comparison, were less susceptible to damage by Lepidoptera but varied in susceptibility to damage by T. tabaci . The best regression models for predicting damage rating, without including the effect of variety, included one measure of seasonal pest total and one plant parameter, head weight. Further regression analysis showed that, in most cases, the relationship of seasonal pest total to damage had the same slope for all varieties but different intercepts. This result indicates that, at a given population density, the models predict different damage ratings for the varieties, implying that nonpreference is not the only resistance mechanism operating and that mechanisms involving tolerance or antibiosis were involved. Use of regression models that test for varietal differences in the relationship of plant parameters and pest population densities to damage would be helpful in designing good assays of resistance for selection of new breeding lines.

Analysis of Resistance in Cabbage Varieties to Damage by Lepidoptera and Thysanoptera

Inbreds and hybrid cabbage (Brasica oleracea var. capitata) selected for resistance to diamondback moth (DBM, Plutella xylostella L.) were tested in the field in New York and Honduras for resistance. In New York, plants were inoculated with up to 400 eggs per plant to enhance the severity of the tests. In Honduras, where natural populations of DBM were high, especially in the dry season, there were three distinct classes of susceptibility to DBM: the very susceptible controls or standard cultivars, the higher resistant glossy-leaved lines, and the intermediate selections with normal leaf bloom (...)

/pdf/selection-for-resistance-to-diamondback-moth-plutella-o908ioht8j.pdf

Selection for Resistance to Diamondback Moth (Plutella xylostella) in Cabbage

Mist-chamber, field, and detached leaf inoculation procedures identified plants resistant to bacterial soft rot [Erwinia carotovora subsp. carotovora, (Ecc)] in Brassica rapa and related species. The mist-chamber seedling inoculation provided the best correlation of mean disease severity ratings with the field plant inoculation (r = 0.67**) and was used to identify resistant materials. The optimum mist-chamber incubation conditions to distinguish the resistance of accessions were 23 °C and 100% RH and were used for primary screening. A total of 752 accessions of B. rapa and related Cruciferae were screened. In general, accessions of B. oleracea were more resistant than accessions of B. rapa. Within B. rapa, subspecies pekinensis and chinensis were more susceptible than other subspecies. No completely resistant material was found. In species of B. rapa, only 7% of accessions showed some degree of resistance with plant-to-plant variation within the accessions. G30444, G30449, and AVRDC2837 were identified as the most resistant materials in B. rapa by both mist-chamber and field inoculations. The resistance was correlated between an USA isolate (Geneva-1) and two Chinese isolates (RL4-1 and RL-19) of Ecc.

M. H. Dickson

Papers

Regional variation in Brassica nigra and other weedy crucifers for disease reaction to Alternaria brassicicola and Xanthomonas campestris pv. campestris

Two Types of Resistance to the Diamondback Moth (Lepidoptera: Plutellidae) in Cabbage

Analysis of Resistance in Cabbage Varieties to Damage by Lepidoptera and Thysanoptera

Selection for Resistance to Diamondback Moth (Plutella xylostella) in Cabbage

Screening and identification of resistance to bacterial soft rot in Brassica rapa.