Levels of host plant resistance to banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), in African Musa germplasm

Forty-five Musa clones, including endemic and introduced cultivars plus hybrids, were evaluated for resistance against the banana weevil, Cosmopolites sordidus, in a field trial in Uganda. The predominant groups of staple crops, East African highland bananas (Musa spp. AAA) and plantains (Musaspp. AAB), as well as plantain-derived hybrids (AAB × AA), showed the highest levels of susceptibility to this pest. These were followed by dessert bananas (Musa spp. AAA), exotic bananas (Musa spp. ABB) and finally diploids of M. acuminata (AA). Hybrids of banana origin were highly resistant. Some East African highland cultivars, especially brewing types (e.g., Kabula, Bagandeseza, Ediirira), showed intermediate levels of resistance. Among the non-highland bananas, high levels of resistance were observed in Yangambi-Km5 (AAA), Cavendish (AAA), Gros Michel (AAA), Kayinja (ABB, Pisang Awak subgroup), Ndiizi (AB, Ney Poovan subgroup)and Kisubi (Ney Poovan subgroup). The highest resistance was observed in banana hybrids TMB2×7197-2, TMB2×8075-7 and the wild banana Calcutta-4 (AA). These were considered the best sources of resistance for a weevil resistance-breeding programme with the two hybrids commonly used as improved male parents. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigations on possible mechanisms of resistance to nematodes in Musa

Summary The burrowing nematode (Radopholus similis) is one of the major nematode species attacking banana and plantains. Sources of resistance to this nematode were found and studies were made of the resistance mechanisms involved. Relatively greater numbers of preformed phenolic cells were found in roots of the resistant and intermediately resistant cultivars Yangambi km5 and Gros Michel than others. However, in another resistant cultivar, Pisang Jari Buaya, fewer phenolic cells were found, but this clone had high numbers of cells with lignified walls suggesting a different mechanism of resistance. An interesting correlation was found between level of susceptibility to R. similis and root dry matter. A possible role of lignin in resistance to R. similis in Musa is also indicated.     

Field screening ofPisum accessions to evaluate their susceptibility to the pea weevil (Coleoptera: Bruchidae)

Summary Seventeen unreplicated field trials over nine sites and four years were used to classifyPisum germplasm (P. sativum L. &P. fulvum Sibth. & Sm) as potential sources of resistance to the pea weevil,Bruchus pisorum (L.). The emergence of adult weevils from <10% of harvested seed was used as the selection criterion to indicate possible resistance. A total of 1900Pisum accessions were assessed using the field trials and 1754 of theP. sativum accessions were eliminated. However in the 18P. fulvum accessions screened, the level of infestation by pea weevil was always below the arbitrary resistance threshold selected. This suggests thatP. fulvum accessions could be a valuable source of resistance to the pea weevil.     

Cytoplasmic genetic diversity in bananas and plantains

Summary Concerns over yield declines in bananas and plantains due to the spread of Black Sigatoka disease in Musa have drawn attention to the collection of Musa germplasm and its use in conventional and biotechnological improvement programs. This report demonstrates the use of chloroplast DNA (cpDNA) restriction fragment length polymorphisms (RFLPs) for differentiating cytoplasms of various Musa clones. DNA was extracted from lyophilized leaf blade tissue and digested with either Eco R1, Hind III, Bam H1 or Pst I. Southern blots onto nylon membranes were probed with radioactively labeled heterologous orchid and lettuce cpDNA fragments. Among the 14 Musa clones examined, a single balbisiana and four acuminata-type cytoplasms were differentiated. The ability to distinguish between cytoplasms and to place plants within a cytoplasmic grouping demonstrates the usefulness of RFLP technology in evaluating diversity and determining the ancestry of Musa clones.     

Nematode resistance in bananas: screening results on some new Mycosphaerella resistant banana hybrids

Banana hybrids with resistance to Yellow Sigatoka and Black Leaf Streak disease were evaluated for resistance to the burrowing nematode Radopholus similis and to the lesion nematode Pratylenchus coffeae in a growth chamber at 24–28°. Plants produced by tissue culture were acclimatised for 6 weeks prior to inoculation. Forty-five days after inoculation with nematodes, the root systems were processed and nematode numbers assessed. Two cultivars of Grande Naine (Musa AAA, Cavendish subgroup, ITC1256 and cv902) and one cultivar of Yangambi Km5 (Musa AAA, Ibota subgroup, ITC1123) were used respectively as susceptible and resistant controls. Results based on multiplication rates and root infestations showed that three of these hybrids (FB918, FB919 and FB924) were not significantly different from the resistant control Yangambi Km5 with a lower multiplication of R. similis. Similarly four of these hybrids (FB918, FB919, FB920, FB924) showed a lower multiplication of P. coffeae, not significantly different from the same resistant control. This is the first study that shows a partial resistance to both nematode species, R. similis and P. coffeae within synthetic hybrids of M. acuminata, adding an important extra value to these dessert banana hybrids formerly bred to resist to Mycosphaerella leaf spot diseases.     

Breeding alfalfa cultivars resistant to the alfalfa weevil

A ten-year study consisting of nine field experiments was conducted to evaluate alfalfa (Medicago sativa L.) for resistance to larval feeding by the alfalfa weevil (Hypera postica Gyllenhal). The results were consistent over years and experiments. Only one source of alfalfa germplasm, designated Starnes, showed resistance to larval feeding in the field under natural infestations of the weevil. The cultivars Team, Arc, and Liberty have been developed from this germplasm source. The only effective method of selection for field resistance to the weevil was field selection under natural weevil infestations. Selection was based on low larval feeding on spaced plants. After six generations of such selection the Starnes germplasm showed only one-third as much defoliation as did the check cultivars. The heritability of the weevil resistance was moderately high. Field resistance was transferred to other strains through hybridization; hybrids were intermediate to the resistant and susceptible parents. Resistance was stable.Laboratory and greenhouse efforts to breed alfalfa weevil resistant alfalfa-using such techniques as adult cotyledon-nonpreference tests, adult leaf-feeding tests, larval-growth and survival tests, oviposition-stimulus tests, and oviposition-nonpreference tests-have failed to produce field resistance.Paper No. 5308 of the Journal series of North Carolina Agricultural Experiment Station, Raleigh, N. C., in cooperation wich ARS, USDA. Received 15 June 1977.     

The potential of high-resolution BAC-FISH in banana breeding

The genetic complexity in the genus Musa has been subject of study in many breeding programs worldwide. Parthenocarpy, female sterility, polyploidy in different cultivars and limited amount of genetic and genomic information make the production of new banana cultivars difficult and time consuming. In addition, it is known that part of the cultivars and related wild species in the genus contain numerous chromosomal rearrangements. In order to produce new cultivars more effectively breeders must better understand the genetic differences of the potential crossing parents for introgression hybridization, but extensive genetic information is lacking. As an alternative to achieve information on genetic collinearity we make use of modern chromosome map technology known as high-resolution fluorescent in situ hybridization (FISH). This article presents the technical aspects and applications of such a technology in Musa species. The technique deals with BAC clone positioning on pachytene chromosomes of Calcutta 4 (Musa acuminata ssp. burmanicoides, A genome group, section Eumusa) and M. velutina (section Rodochlamys). Pollen mother cells digestion with pectolytic enzymes and maceration with acetic acid were optimized for making cell spread preparations appropriate for FISH. As an example of this approach we chose BAC clones that contain markers to known resistance genes and hybridize them for establishing their relative positions on the two species. Technical challenges for adapting existing protocols to the banana cells are presented. We also discuss how this technique can be instrumental for validating collinearity between potential crossing parents and how the method can be helpful in future mapping initiatives, and how this method allows identification of chromosomal rearrangements between related Musa species and cultivars.     

Inheritance and allelism of resistances to the Russian wheat aphid in seven wheat lines

Summary Studies were conducted to determine the inheritance and allelic relationships of genes controlling resistance to the Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), in seven wheat germplasm lines previously identified as resistant to RWA. The seven resistant lines were crossed to a susceptible wheat cultivar Carson, and three resistant wheats, CORWA1, PI294994 and PI243781, lines carrying the resistance genes Dn4, Dn5 and Dn6, respectively. Seedlings of the parents, F₁ and F₂ were screened for RWA resistance in the greenhouse by artificial infestation. Seedling reactions were evaluated 21 to 28 days after the infestation using a 1 to 9 scale. All the F₁ hybrids had equal or near equal levels of resistance to the resistant parent indicating dominant gene control. Only two distinctive classes were present and no intermediate types were observed in the F₂ segregation suggesting major gene actions. The resistance in PI225262 was controlled by two dominant genes. Resistance in all other lines was controlled by a single dominant gene. KS92WGRC24 appeared to have the same resistance gene as PI243781 and STARS-9302W-sib had a common allele with PI294994. The other lines had genes different from the three known genes.     

Use of culture-derived Fusarium oxysporum f. sp. cubense, race 1 filtrates for rapid and non-destructive in vitro differentiation between resistant and susceptible clones of field-grown banana

Banana and plantain are among the most important food crops in developing countries but production is threatened by increasing virulent forms of Fusarium oxysporum f. sp. cubense. Chemical control is not economically effective and,therefore, breeding programs are necessary. Traditional field studies of new genotype resistance to this disease are time-consuming and destructive. Therefore,we developed a rapid and non-destructive procedure to differentiate field-grown banana resistant from susceptible clones. This procedure implicates application of culture filtrates of Fusarium oxysporum f. sp. cubense race 1 onto banana leaves. The relationship between duration of the fungal in vitro incubation, and the fungal culture fresh mass, the culture filtrate absorbency, and the Gross Michel (susceptible cultivar)leaf lesion area (after application of the culture filtrate) were similar and at 24day-incubation the highest values of the recorded indicators were observed. A comparison between Gross Michel and FHIA-01(resistant) was also performed. The most relevant differences between cultivars were observed at 48 hours after application of the culture filtrate, and in the middle-aged leaves. The position of the culture filtrate application in the leaf limb (distal, middle, proximal) was not determinant. A wider comparison among banana cultivars confirmed previous results informed by other researchers using different systems to study this plant-fungus interaction. Such a confirmation validates the effectiveness of the procedure described here to select rapid and non-destructively banana resistance to this disease at field level. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of the black sigatoka resistance locus bs 1 and ploidy level on fruit and bunch traits of plantain-banana hybrids.

Summary Plantain (Musa spp., AAB group) cultivation is threatened by black sigatoka, an airborne fungal (Mycosphaerella fijiensis Morelet) leaf spot disease. Several traits in plantains and bananas are mainly affected by major genes. The host resistance response to black sigatoka is under the control of at least three different genes, one major recessive gene bs ₁ and two other independent additive alleles. Diploid and tetraploid plantain hybrids were evaluated for bunch weight, fruit weight, fruit length and fruit circumference. The F₁ euploid hybrids were derived from interspecific crosses between the resistant diploid wild banana Calcutta 4 and the susceptible triploid plantain cultivars Obino l'Ewai and Bobby Tannap. Linear and multiple regression models, coefficients of determination, and Durbin-Watson statistics were used to determine the single and combined effects of the major locus for black sigatoka resistance and ploidy on the different traits in the progenies. Differences in yield were mainly due to changes in weight and girth of fruit, which are affected by black sigatoka disease. The combined effect of ploidy and resistance to black sigatoka was partially responsible for the quantitative trait variation in yield. As a result of the gene interaction in the black sigatoka resistance locus bs ₁, the partially resistant and less susceptible phenotypes showed higher yield than their more susceptible full sibs.     

Inheritance of resistance to damage byThrips tabaci Lindeman (Thysanoptera: Thripidae) in Cabbage

Summary The inheritance of resistance in cabbage (Brassica oleracea var.capitata) to damage caused byThrips tabaci Lindeman was studied in progeny from four crosses between resistant and susceptible inbred lines. In two families sharing the same susceptible parent, the narrow-sense heritability was calculated to be high (>90%), using the Warner method of calculation (Warner, 1952). The other two families, also sharing a susceptible parent, had very low narrow-sense heritability (0–11%). In three of the four families, however, the validity of the Warner calculations were called into question due to significant epistatic interactions. In all four families, the F₁ populations approached or exceeded the susceptibility of the susceptible parent, indicating that susceptibility is generally dominant. The importance of epistasis and dominance suggests that tests of hybrid combinations to determine combining ability for thrips resistance may be required, rather than selecting only on the basis of thrips damage to the inbred lines. The technique of planting wheat upwind from the cabbage test plot did generate adequate levels of thrips pressure, but the infestation was uneven in two of the four blocks, so that reasonable replication of tests is required.     

Biochemical markers for cabbage seedpod weevil (<Emphasis Type="Italic">Ceutorhynchus obstrictus</Emphasis> (Marsham)) resistance in canola (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

In the last decade, the cabbage seedpod weevil (Ceutorhynchus obstrictus (Marsham)) has become a major insect pest of canola (Brassica napus L.) in Canada reducing seed yields up to 35%. Therefore, the benefits of developing weevil resistant germplasm to canola breeders and the industry would reduce input costs, pesticide use, environmental degradation and increase yield. Yellow mustard (Sinapis alba L.) is resistant to C. obstrictus (CSPW), although the exact mechanism is not known (McCaffrey et al. 1999). A unique canola population was generated at the University of Guelph from a cross between B. napus and S. alba through embryo rescue and backcrossed to canola several times prior to double haploid (DH) production. Approximately one-half of this DH population had canola quality glucosinolate concentration (<16 μmol/g) and was used for further breeding. The hypothesis was that some DH progeny from this cross inherited resistance to CSPW from S. alba. Weevil infestation levels were assessed for the B. napus × S. alba BC2 and BC3 DH populations in the field over 7 years in Alberta where weevil pressure is strong to establish the resistant or susceptible status of these lines. The basic objectives for this study were to confirm field resistance in the B. napus × S. alba germplasm in Ontario and to identify any biochemical markers associated with resistance/susceptibility. Canola doubled haploid lines derived from BC2 or BC3 families were field screened for resistance (R) followed by chemical analysis of glucosinolates to detect biochemical polymorphisms correlated with CSPW resistance using High Performance Liquid Chromatography (HPLC). Two polymorphic peaks were found, one each, from extracts of upper cauline leaves and Stage 3 pod seed, with retention times of ~23 and 19 min, respectively. These HPLC peaks consistently correlated with larval infestation data and the peak differences between R and S DH lines were significant. Therefore, these two peaks can be considered as biochemical markers in this breeding germplasm and may play a role in rapid and early detection of CSPW resistance.     

RFLP characterization of Indian Musa germplasm for clonal identification and classification

Summary Nineteen single-copy clones isolated from a PstI genomic library (cv. Maiden Plantain), and eight Vigna chloroplast DNA clones were used to probe total genomic DNA digests of 57 genotypes of Musa from India. The 19 genomic clones detected a total of 107 polymorphisms among the 57 genotypes. Principal coordinates and phenetic analyses of these data placed cultivars and species into distinct groups that were in general agreement with a previously published RAPD-based classification of these same plant materials. The 107 polymorphisms were sufficient to differentiate each clone from every other clone. Heterologous Vigna chloroplast DNA probes were used to characterize the cytoplasm of Musa cultivars and species. PCO analysis of these RFLPs were detected both within and between the generally recognized genome groups, indicating multiple hybridization pathways in the origin of hybrid clones. Data presented demonstrate that RFLPs are sufficiently abundant to classify Musa germplasm and that genetic relationships among Musa cultivars, based upon RFLP data, are in general agreement with relationships determined by analysis of morphology and RAPDs.     

Selection parameters for resistance to Fusarium oxysporum f. sp. cubense race 1 and race 4 on diploid banana (Musa acuminata Colla)

Summary Shoot tip cultures from banana clones susceptible and resistant to Fusarium oxysporum f. sp. cubense (FOC) race 1 and race 4 were grown in vitro in the presence of different concentrations of fusaric acid and fungal crude filtrates or inoculated with a conidial suspension of FOC to assess correlation between in vivo and in vitro behaviour. Explants were susceptible to both filtrate and fusaric acid irrespective to their known field resistance/susceptibility response. No clear linkage between in vivo and in vitro behaviour was observed and our results suggest that the use of crude filtrate or non-host specific toxin (fusaric acid) in a screening programme for selecting a novel resistant genotype of Musa to FOC is not feasible. When peroxidase activity was used as a parameter to discriminate between sesceptibility and tolerance, results were in good agreement with field response of host plant to pathogens. Early enzymatic activity increased in the incompatible host-pathogen interaction but not in the compatible interaction.Abbreviations IBA Indolebutyric acid - 2iP 6-dimethylallylamino-purine - VCG Vegetative Compatibility Group - FOC Fusarium oxysporum f. sp. cubense - IEF isoelectrofocusing     

Nematode resistance in bananas: screening results on some wild and cultivated accessions of Musa spp.

Bananas cultivated for export all belong to Cavendish cultivars and are all recognized as very susceptible to nematodes, particularly to the burrowing nematode Radopholus similis and the lesion nematode Pratylenchus coffeae. Even if there have been many changes in the management of banana nematodes in large commercial banana plantations, chemical control still remains most often the last resort method to manage the nematodes, although the number of registered products is definitely declining. Therefore, nematode control though genetic improvement is gaining new interest worldwide. In this study, 55 banana accessions mostly diploids from the Musa acuminata genome group (AA) but including some triploid accessions (AAA), some diploids of the Musa balbisiana genome group (BB) and some interspecific hybrids (AAB, AB) were evaluated for resistance to four nematode species R. similis, P. coffeae, Meloidogyne incognita and M. arenaria. These experiments were conducted in a growth chamber under controlled conditions. All banana accessions were susceptible to nematode species, although many different levels of susceptibility were detected. This study confirmed the good resistance status to R. similis of some cultivars from the Pisang jari buaya and Pisang batuau subgroups and the partial resistance of 17 diploid accessions significantly different from the susceptible reference cv. Grande Naine. This study also showed that 12 diploid accessions exhibited a partial resistance to P. coffeae, including some usual or potential genitors belonging to the wild diploids subspecies burmannica (cvs. Long Tavoy 1 and 2) and burmannicoides (cv. Calcutta 4). No source of resistance to Meloidogyne spp. was found. These screening results, combining for the first time four nematode species, are discussed within the scope of banana breeding in order to produce parental diploid lines with single or combined nematode resistances and further develop triploids that can substitute existing susceptible commercial cultivars.     

Mechanisms of Resistance to Tobacco Cutworm (Spodoptera litura F.) and their Implications to Screening for Resistance in Groundnut

Summary The Tobacco cut worm (Spodoptera litura Fab.), a polyphagous defoliating insect is a major pest on groundnut in Asia. Screening germplasm for resistance to Spodoptera litura in the field under high infestation revealed significant genotypic variation. Low damage was observed on Mutant (28-2), NC Ac 343, ICGV 86031, R 9227 and TAG 24. In the laboratory rearing of insect, the resistant genotypes, NC Ac 343, Mutant 28-2 and R 9227 affected larval growth and survival, pupal development, adult emergence and fecundity indicating antibiosis as the principal mechanism of resistance. The reduction in larval weight reared on ICGV 86031 could be due to the toughness of leaves. Though the genotype TAG 24 suffered low damage in the field, the larval and pupal development was normal in the laboratory revealing avoidance/non-preference as the mechanism of resistance. Based on the insight gained from the growth and development of the insect on resistant genotypes, the gain in weight (GIW) of the pre-starved larvae was assessed for its suitability in rapid screening. GIW in 24 h by III instar larvae fed with fully expanded II leaf was found suitable in screening for resistance based on antibiosis. The method could be adopted for screening large breeding populations in a short time under laboratory conditions. The resistant genotypes with different mechanisms of resistance could be hybridized to pool the resistant genes for enhancing the level and effectiveness of resistance in the management of the pest.     

Genetic analysis of resistance to <Emphasis Type="Italic">soil-borne wheat mosaic virus</Emphasis> derived from <Emphasis Type="Italic">Aegilops tauschii</Emphasis>

Genetic Analysis of Resistance to Soil-Borne Wheat Mosaic Virus Derived from Aegilops tauschii. Euphytica. Soil-Borne Wheat Mosaic Virus (SBWMV), vectored by the soil inhabiting organism Polymyxa graminis, causes damage to wheat (Triticum aestivum) yields in most of the wheat growing regions of the world. In localized fields, the entire crop may be lost to the virus. Although many winter wheat cultivars contain resistance to SBWMV, the inheritance of resistance is poorly understood. A linkage analysis of a segregating recombinant inbred line population from the cross KS96WGRC40 × Wichita identified a gene of major effect conferring resistance to SBWMV in the germplasm KS96WGRC40. The SBWMV resistance gene within KS96WGRC40 was derived from accession TA2397 of Aegilops taushcii and is located on the long arm of chromosome 5D, flanked by microsatellite markers Xcfd10 and Xbarc144. The relationship of this locus with a previously identified QTL for SBWMV resistance and the Sbm1 gene conferring resistance to soil-borne cereal mosaic virus is not known, but suggests that a gene on 5DL conferring resistance to both viruses may be present in T. aestivum, as well as the D-genome donor Ae. tauschii.     

Expression of mature plant resistance to Striga hermonthica in maize

Twelve maize genotypes with different degrees of resistance were evaluated in plots inoculated with seeds of the phytoparasite Striga hermonthica (Del.) Benth. and in Striga-free (control) plots for three seasons between 1991 and 1993. Resistant genotypes, although showing similar levels of underground infection as susceptible 9 weeks after maize planting (WAP), had significantly fewer emerged parasitic plants and sustained lower damage. Host damage was not determined by the severity of infection. Percent height and dry matter reductions increased from 3 to 6 WAP for resistant and susceptible genotypes. While percent height and dry matter reductions for resistant genotypes declined at 9 and 12 WAP, susceptible genotypes either maintained or increased their levels of damage. Correlation between the severity of height and dry matter reductions at the vegetative (3 and 6 WAP) and reproductive (9 and 12 WAP) stages of maize growth were not significant, indicating that damage at early stages of growth cannot be used to predict mature plant response. Maize damage score (1–9) at 8 WAP, a non destructive and composite shoot indicator of host performance under Striga infestation, was significantly correlated (r = 0.88, r = 0.82; p < 0.01) to the level of shoot reduction at mature plant stages. Emerged Striga count at 8 WAP was significantly correlated (r = 0.98, p < 0.01) to the count at 10 WAP, the time when parasite emergence was highest. Under high and uniform infestation, mature plant resistance can be detected at 8 WAP, the onset of flowering in maize. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development of common bean (Phaseolus vulgaris L.) lines resistant to the bean pod weevil,Apion godmani Wagner,in Central America

Summary The larva of the bean pod weevil (BPW), Apion godmani Wagner (Coleoptera: Curculionidae), causes serious yield losses in common bean (Phaseolus vulgaris L.) in Mexico and Central America, by consuming the seed as it develops in the immature pod. Resistance to the BPW was identified in bean germplasm of highland Mexican origin, and these sources of resistance were incorporated into a pedigree breeding program to recover locally adapted lines resistant to Bean Common Mosaic Virus and BPW, with commercial grain for Guatemala, Honduras and El Salvador. These lines yielded as well as or better than local cultivars in the absence of the insect, and better than local cultivars when the BPW was present. Resistance appeared to be governed by several genes, and was stable across geographic areas, seasons and planting systems.