Genetic analysis of,and selection for,factors affecting quantitative resistance to Xanthomonas campestris pv. oryzae in rice

Summary This study assessed 46 potato cultivars, breeding lines and Solanum spp. for heat-tolerance using short-term growth rates and carbon assimilation measurements of young in-vitro-derived plants. Plants of the 46 clones and species were transferred from greenhouse conditions to controlled conditions set at 33/25°C day/night with 12 h photosynthetic photon flux density (PPFD) at 430–450 mol m^-2s^-1 and an 8 h daylength extension (6 mol m^-2s^-1), to inhibit tuberization. Twenty eight accessions were also grown in a 20/10°C controlled environment. Plants were harvested after 10 and 20 days and dry weights of the plant components were measured for plant growth analysis. Gas exchange (leaf net photosynthesis and maintenance dark respiration) and leaf chlorophyll fluorescence parameters (O, P, and T) were measured at 30°C. Amongst the 30 accessions grown at both hot and cool temperatures, only two accessions (Yungay and AVRDC 1287.19) produced more dry weight in the hot chamber than the cool chamber. Hot/cool ratioss for net assimilation rate (NAR) and relative growth rate (RGR) exceoded unity in five and six accessions, respectively. For the 46 accessions grown under hot conditions, none had significantly greater values than those of the control clones for RGR and NAR. Differences between clones in maintenance respiration and net photosynthesis were more closely related to RGR, NAR, and total dry weight (TDWT) in clones which invested more dry weight in leaves and less in stems. Attributes of the chlorophyll fluorescence curve did not explain more of the clonal variation in RGR, NAR, and TDWT than did gas exchange parameters. No single gas exchange or fluorescence character explained more than 50% of the variability among clones for NAR, RGR, or TDWT, but combination of favourable attributes could improve potato heat tolerance in the future.     

Evidence of a partial reproductive barrier between wild and cultivated pearl millets (Pennisetum glaucum)

Summary The occurrence of seed malformation in association with reduced thousand grain weight and germination ability has been observed in crosses between cultivated female plants and wild male plants. A survey of 16 cultivated accessions (P. glaucum subsp. glaucum) and 11 wild accessions (P. glaucum subsp. monodii) ranging over the whole species diversity showed this postzygotic incompatibility was general, but its intensity varied greatly with the cultivated female accession used and very little with the wild male parent origin. About 15% of the 123 cultivated x wild crosses observed gave normal seeds. Seed malformation has never been observed in crosses between cultivated accessions and appeared independent of genetic distances between the parents. The reciprocal crosses between wild female plants and cultivated male plants gave normal-looking seeds with good germination but consistently reduced thousand grain weight. Both seed malformation and seed small size are an expression of a genetic imbalance. These slight reproductive barriers seem to have been built during the domestication process.Abbreviation ICRISAT International Crop Research Institute for the Semi-Arid Tropics     

Antibiosis mechanism of resistance to pod borer, Helicoverpa armigera in wild relatives of chickpea

The pod borer, Helicoverpa armigera, is one of the major constraints to chickpea production worldwide. The levels of resistance to pod borer in the cultivated chickpea germplasm are moderate, and therefore, we studied the reaction of 32 accessions of wild relatives of chickpea for resistance to H. armigera under greenhouse conditions. Accessions ICC 17257, IG 70002, IG 70003, IG 70012, (Cicer bijugum), IG 69948 (C. pinnatifidum), IG 69979 (C. cuneatum), IG 70032, IG 70033, IG 70038, and IG 72931 (C. judaicum) showed lower leaf feeding, a drastic reduction in larval weight, and poor host suitability index at the vegetative and/or flowering stages of crop growth as compared to the cultivated chickpeas. Based on percentage pods damaged by 5th day (< 52% pods damaged compared to 90% pods damaged in Annigeri), and percentage weight gain by the larvae (< 35% weight gain compared to 366% weight gain on ICCV 2); accessions IG 69979 (C. cuneatum), IG 70003, IG 70022, IG 70016, IG 70013, IG 70012, IG 70010, IG 70001, IG 70018, and IG 70002 (C. bijugum), and IG 72953 (C. reticulatum) showed high levels of resistance to H. armigera. Larvae of H. armigera weighed < 50 mg when reared on C. pinnatifidum (IG6 9948 and IG 70039), and C. judaicum (IG 72931) compared to 301.95 mg on C. arietinum (ICCC 37 – the cultivated chickpea). Larval weights on many accessions of the wild relatives of chickpea were much lower than those on the cultivated chickpeas, indicating the existence of different mechanisms of resistance to H. armigera. There was no pupation and adult emergence when the larvae were reared on accessions of C. pinnatifidum (IG 69948 and IG 70039), and C. judaicum (IG 69980, IG 70032, IG 70033 and IG 72931). The wild relatives of chickpea showing high levels of antibiosis to H. armigera can be used to introgress diverse resistance genes into cultivated chickpea to increase the levels and diversify the basis of resistance to this insect. An erratum to this article is available at .     

Growth analyses of tomato genotypes grown under low night temperatures and low light intensity

Summary In three experiments the growth of 16 genotypes of tomato was examined. The plants were raised in growth rooms at a day temperature of 19°C and night temperatures of 14, 10 or 6°C respectively under a light intensity of 24 Wm^-2 visible radiation and a daylength of 8 hours. The results were analysed by a multivariate analysis of variance.Relative growth rate (RGR), leaf area ratio (LAR), specific leaf area (SLA) and leaf weight ratio (LWR) decreased with time. The change in net assimilation rate (NAR) was small. The decrease in RGR was mainly due to the decrease in LAR.RGR, LAR and SLA were lower and LWR slightly higher at lower night temperatures. NAR was hardly affected. The lower RGR at lower night temperatures was mainly due to a lower SLA.Significant differences between genotypes were found in total dry weight, NAR, LAR, SLA and LWR, but hardly in RGR. Significant genotype × temperature interactions occurred.LAR and SLA were positively, NAR and LAR, and NAR and SLA negatively correlated.     

Analysis of differences in growth of cucumber genotypes under low light conditions in relation to night temperature

Summary Growth of four breeding lines and two cultivars of slicing cucumber with different growth at low temperature and light intensity was analysed in relation to night temperature. Plants were grown from 17 days after sowing at 20°C day temperature and 20, 15 or 10°C night temperature (NT), a light intensity of 24 W/m² visible radiation and a daylength of 8 hours. Data from six successive harvests, ending 47 days after sowing, were analysed according to a MANOVA procedure.RGR, NAR, LAR, SLA and LWR generally decreased with time. Ln W and RGR were largely similar at 20 and 15°C NT, but reduced at 10°C NT. LAR and SLA decreased at each lower NT, whereas LWR increased. NAR was only marginally affected by NT. Significant genotypic differences occurred for 1n W, LAR, SLA, LWR, stem length and percentage of dry matter in leaves and stems at all NT's and for RGR and NAR only at 20°C. Genotypic differences for 1n W could not be explained by differences for RGR, but by differences for initial plant weight.Significant genotype × night temperature interactions were present for LWR. Breeding lines increased LWR in response to lower NT, while that of cultivars remained fairly constant. Implications for breeding are discussed.Abbreviations and definitions L plant length - LA leaf area - W dry weight of the shoot - RGR relative growth rate (the increase in W per unit of time and unit of W) - NAR net assimilation rate (the increase in W per unit of time and unit of LA) - LAR leaf area ratio (the leaf area at time t per unit of W) - SLA specific leaf area (the leaf area at time t per unit of leaf weight) - LWR leaf weight ratio (the leaf weight at time t per unit of W) - RGR NAR × LAR - LAR SLA × LWR - MANOVA multivariate analysis of variance     

Development of bio-assays and screening for resistance to beet armyworm (Spodoptera Exigua Hübner) in Allium cepa L. and its wild relatives

The beet armyworm (Spodoptera exigua Hübner)is the most important pest in tropical Alliumcultivations. All shallot (Allium cepa L. group Aggregatum) cultivars are susceptible to this pest. Therefore accessions from three wild Alliumspecies, namely A. galanthum Kar. et Kir., A. fistulosum L. and A. royleiStearn, next to A. cepa L. were used to screen for resistance. First of all, a reliable bio-assay had to be developed. To this end transparent plastic cages with in total 5 plants of one accession per cage were placed on per lite in a heated greenhouse. Five 3-day old larvae were inoculated on each plant. Eight days after inoculation the number of surviving larvae per cage and the mean fresh weightper larva was determined. The lowest larval survival (36%) was found on A. roylei. This was not, however, significantly different from other Allium accessions. Significant differences were found in the fresh weight per larva fed on different Allium accessions. The larvae survived on A. roylei had a very low fresh weight (10.3 mg per larva), while those on an accession of A. fistulosum had the highest fresh weight (45.1 mg per larva). The larval fresh weight on A. roylei was lower than all the other accessions except from the tropical shallot cultivar Bawang Bali. To check whether or not a toxic compound was involved in the resistance present in A. roylei, tenaccessions from four Allium species were screened. Five 3-day old larvae were inoculated on regularly replaced leaf material of each accession ofAllium species. No significant differences were found in mean fresh weight per larva and mean survival of larvae among different accessions. There were also no significant differences in pupal weight and developmental time. All larvae became pupae 10 days after inoculation. The data indicate that there is no toxic compound present in A. roylei. These results are underlined by the observation in the greenhouse bio-assay that A. roylei plants were equally damaged by the beet armyworm compared to otherAllium species. The results obtained so far therefore suggest that introduction of resistance to S. exigua via the exploitation of variation for resistance to the beet armyworm in A. roylei is unclear and that genetic engineering using Cry sequences could provide a way forward. This revised version was published online in July 2006 with corrections to the Cover Date.     

Random amplified polymorphic DNA (RAPD) variation in Fagopyrum tataricum Gaertn. accessions from China and the Himalayan region

The diversity among 52 landraces and cultivars of tartary buckwheat (Fagopyrum tataricum Gaertn.) and one accession of its wild ancestor, F. tataricum ssp. potanini Batalin, from diverse geographic origins was examined using random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) markers. Eighteen primers produced a total of 240 fragments, of which 153 (63.75%) were monomorphic and 87 (36.25%) polymorphic bands. UPGMA-based pairwise Jaccard’s coefficient of similarity was used to deduce the relationships among 53 genetically diverse accessions. The similarity between cultivated tartary buckwheat accessions ranged from 0.61 to 1.00. Four distinct clusters were formed which corresponded well with the geographic distribution of the tartary buckwheat. Nepalese accessions showed maximum diversity followed by Chinese accessions. Tartary buckwheat accessions from the Himalayan region of northwestern India revealed a narrow gene pool. The wild buckwheat accession did not group with any of the three cultivated tartary buckwheat groups, and formed its own single-entry group. Genetic similarity (0.59) of Chinese buckwheat accessions with the wild ancestor reaffirmed that cultivated tartary buckwheat originated in the Yunnan province of northwestern China. Consistent with some earlier reports, our study demonstrated the usefulness of the RAPD technique for the characterization of plant genetic resources and assessment of diversity between species. This revised version was published online in August 2006 with corrections to the Cover Date.     

A genomic library of Lycopersicon pennellii in L. esculentum: A tool for fine mapping of genes

The cultivated tomato contains only a small fraction of the genetic variation present in its wild relatives. In order to use the wild germplasm in tomato breeding and genetic studies we developed a new kind of genetic resource which is composed of 50 L. esculentum lines each containing a single introgression from the green fruited species L. pennellii (LA 716). Each of the introgression lines is nearly isogenic to the cultivated tomato; these lines provide complete coverage of the wild species genome. The lines contain on the average an introgression of 33 cM from a total genome size of 1200 cM. The size and identity of the introgressed segments was determined based on RFLP analysis of 350 markers. This resource can be viewed as a genomic library of the wild species in the cultivated background. It covers the entire genome with single independent inserts per line and therefore every phenotypic difference between the introgression lines can be associated with the unique introgressed segment. The development and potential application of this resource are discussed.     

Species relationships in the subgenus Ceratotropis (genus Vigna) as revealed by RAPD analysis

Summary The genetic variation among 23 accessions of 5 species in the subgenus Ceratotropis, genus Vigna, were investigated by random amplified polymorphic DNA (RAPD) analysis. A total of 404 fragments amplified with 24 primers were scored and analyzed by cluster analysis. The accessions used were separated into two main groups with an average of 70% differences. Within the main groups, five subgroups were recognized, which are in complete agreement with taxonomic species. Wild forms were always grouped with their most closely related cultivated forms and they showed variation in each species. The largest intraspecific variation was found in V. radiata (mungbean), in which wild forms (V. radiata var. sublobata) were highly different from each other and from cultivated forms. V. angularis (adzuki bean) showed the least variation and thus, was probably differentiated in relatively recent times.     

The reproductive biology of okra. 1. Study of the breeding system in four Abelmoschus species

Summary The breeding system of Abelmoschus species is not well known. Although being self-compatibles allogamy reaches 63%. The aim of the study was to place four Abelmoschus species on the log P/O scale devised by Cruden (1977). On this scale P = pollen grains per anther × anthers per flower and O = ovules production. Pollens and ovules productions were therefore assessed for 68 accessions of two cultivated species, A. esculentus and A. caillei, and two wild, A. manihot and A. moschatus. Extreme log P/O values ranged from 1.69 for the variety Clemson Spineliss (A. esculentus) to 2.94 for ORS 278 (A. manihot). Averages of wild species A. moschatus (2.17) and A. manihot (2.19) indicate facultative autogamy. Averages for cultivated species A. esculentus (2.00) and A. caillei (2.05) suggest more autogamy.     

Resistance toPhytophthora porri in leek and some of its wild relatives

Summary Winter leek and related plant material was evaluated for resistance to white tip disease (Phytophthora porri) in the Netherlands. Significant differences in partial resistance were found between winter leek accessions in field tests with zoospore and natural inoculation. These differences were consistent over three years, and indicate that resistance can be improved through mass selection in winter leek cultivars. Some accessions of wild or cultivated relatives of winter leek with higher levels of resistance were found in a glasshouse test with zoospore inoculation. These sources of resistance were also highly resistant in field experiments over a two year period.     

Introgression of in vitro regeneration capability of Lycopersicon pimpinellifolium Mill. into recalcitrant tomato cultivars

The goal of this research was to study the introgression of the high regeneration capacity of Lycopersicon pimpinellifolium Mill line WV-700, in recalcitrant tomato cultivars (L. esculentum Mill cvs. Petomech, Santa Rita and VFN-8) using backcrossing. Hypocotyl explants of in vitro germinated seeds were cultivated in half strength MS medium supplemented with 5mg/l 6-BA to assess their shoot regeneration capacity. The apical shoot of the in vitro germinated seeds were cultured on a separate medium. Apical shoots from genotypes showing high regeneration rates were acclimated in a glasshouse and used as pollen donors for the next backcrossing. After four backcrossings, the material showed a similar mean fruit weight for the cultivated tomato and a high regeneration capacity similar to the wild species. It is shown that L. pimpinellifolium can be used with success as donor parent to introgress in vitro regeneration capacity to recalcitrant tomato cultivars. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reaction of Lycopersicon cultivars and wild accessions to tomato leaf curl virus

Summary 1201 tomato cultivars, breeding lines and accessions of Lycopersicon species were screened for tomato leaf curl virus (TLCV) under field and laboratory conditions during summer seasons of 1986 to 1989. Two lines of L. hirsutum (PI 390658 and PI 390659) and 2 lines of L. peruvianum (PI 127830 and PI 127831) were resistant to TLCV infection. These accessions did not produce any leaf curl symptoms either in field or after inoculation by whitefly Bemisia tabaci with TLCV. Adult whiteflies died within 3 days after releasing on resistant accessions (PI 390658, PI 390659, PI 127830), whereas the whiteflies survived upto 25 days on susceptible tomato cultivars. Under field conditions 0–4 and 5–25 adult whiteflies were observed on resistant and susceptible cultivars respectively. Hybridization was effected using the popular tomato cultivars Arka Sourabh, and Arka Vikas, as the female parents and the resistant Lycopersicon wild species as the pollen parents, to incorporate the resistant gene(s) into the edible tomatoes.     

Screening wild Lycopersicon species for resistance to powdery mildew (Oidium lycoperiscum)

Since the late 1980s powdery mildew, designated Oidium lycopersicum, frequently invaded the tomato crop in Western Europe. All commercial cultivars are susceptible. To screen for resistance in wild species a reliable and efficient disease test was developed. Young plants with two to three true leaves are inoculated at high relative humidity by spraying with a freshly prepared suspension of 2×10⁴ conidia, ml^–1. Symptoms are periodically evaluated according to a scale based on the percentage of leaf area with mycelium.One hundred and twenty seven accessions, representing eight wild Lycopersicon species, were screened for resistance to O. lycopersicum. A large variation in resistance was found between species. L. hirsutum was the most resistant species; L. pennellii was moderately resistant; species of the subgeneric group of L. esculentum and of the peruvianum-complex were all susceptible. L. parviflorum was classified separately due to a large variation between accessions. Except for this species, a low variation was found between accessions within species. High levels of resistance were observed in four accessions of L. hirsutum, in one of L. parviflorum and in one of L. peruvianum. This resistance is characterized by a very low disease incidence and a strongly restricted mycelium growth and lack of sporulation.     

Reaction of wild species of the geneus Lens to drought

Summary Susceptibility to drought stress is a key factor in dry land lentil (Lens culinaris Medikus) production in the Mediterranean region of West Asia and North Africa. This study examined the response to drought stress of 121 accessions representing all subspecies of the genus Lens; cultivated, and the wild L. culinaris ssp. orientalis (Boiss.) Ponert, L. culinaris ssp. odemensis (Ladiz.), L. nigricans M.B. Godr. ssp. nigricans Godr. and L. nigricans ssp. ervoides (Brign.) Ladiz. for their potential use in breeding for dry land conditions. Accessions were grown under two moisture regimes (dry land and dry land plus supplemental irrigation) at Breda, Syria during the 1990–91 and 1991–92 seasons. The cultivated lentil had markedly superior seed and straw production than did the wild Lens species. Time to flowering accounted for less than 10% of the variation in yield of wild accessions under rainfed conditions in the two seasons, showing that, in contrast to the cultivated germplasm, drought escape was relatively unimportant in wild lentil. Performance under drought in wild lentil, measured in terms of dry land seed yield or drought susceptibility index (S), was randomly distributed among collection locations with little relation to collection site aridity. Direct selection of wild lentil germplasm for biomass yield under dry conditions is of little value and an evaluation of wild accessions in hybrid combination is needed.     

Diversity in selected wild and cultivated species of pigeonpea using RFLP of mtDNA

Diversity in 28 accessions representing 12 species of the genus, Cajanus arranged in 6 sections including 5 accessions of the cultivated species, C. cajan, and 4 species of the genus Rhyncosia available in the germplasm collection at ICRISAT was assessed using RFLP with maize mtDNA probes. Cluster analysis of the Southern blot hybridization data with 3 restriction enzymes – 3 probe combinations placed the genus Rhyncosia in a major group well separated from all the species belonging to the genus Cajanus. Within the genus Cajanus, the 4 accessions of C. platycarpus belonging to section Rhynchosoides formed a separate group in contrast to those in other sections of pigeonpea. In the section, Cajanus all the 5 accessions of C. cajan were grouped together and C. cajanifolius belonging to the same section was in a subgroup by itself closer to the main group. The four accessions of C. scarabaeoides, were together and the other species belonging to section Cantharospermum were in different subgroups. The intra-specific variation was seen even within accessions of certain pigeonpea wild species such as C. scarabaeoides, C. platycarpus, C. acutifolius, and even the cultivated species of C. cajan. This study suggests that RFLP of mtDNA can be used for the diversity analysis of pigeonpea and it gives some indications on the maternal lineage among the species. The variations in the mitochondrial DNA hybridization patterns also suggest the extensive rearrangement of the organelle genome among the Cajanus species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Variation in developmental patterns of wild barley (Hordeum spontaneum L.) and cultivated barley (H. vulgare L.)

Summary Six wild barley (Hordeum spontaneum) accessions, from a diverse range of habitats, and two spring-cultivated barleys, were examined for variation in durations of development phases. The durations of the leaf initiation and spikelet initiation phases were longer and spikelet growth phases shorter, in wild than in cultivated barley. Across all wild and cultivated barleys the rate and duration of spikelet initiation were negatively correlated, but neither was related to the number of spikelets per spike. The number of spikelets was positively correlated with the number of leaves and the ratio of the number of spikelets to the number of leaves declined with increasing time to anthesis, indicating that each successive leaf was associated with a diminishing increase in the number of spikelets. The duration of culm elongation and final culm length were shorter in accessions of cultivated barley compared with wild barley. This paper also discusses the feasibility for increasing the number of spikelets per spike through breeding for genetic changes in lengths of pre-anthesis phases of development.Abbreviations ANOVA Analysis of variance - HV Hordeum vulgare - CE Culm elongation - DR Double ridge - HS Hordeum spontaneu - ° Cd Degree days     

Inheritance of growth characters of tomato (Lycopersicon esculentum Mill.) under low energy conditions

Summary To study the mode of inheritance of W, RGR, NAR, LAR, SLA and LWR, the growth of 15 tomato genotypes and 104 of their F1's was analyzed. The plants were grown at a 19°C day temperature and a 10°C night temperature under a light intensity of 24 Wm^-2 visible radiation and a daylength of 8 hours. Combining ability analyses of variance revealed highly significant differences in GCA values between parents for all characters studied and significant SCA values for some of the characters. GCA values for NAR and LAR, and for NAR and SLA were strongly negatively correlated. A strong positive correlation existed between GCA values for LAR and SLA. The possibilities for improving growth under low energy conditions by using growth characters in breeding are discussed.Abbreviations W dry weight of the plant - RGR relative growth rate - NAR net assimilation rate - LAR leaf area ratio - SLA specific leaf area - LWR leaf weight ratio - MANOVA multivariate analysis of variance - GCA general combining ability - SCA specific combining ability     

Response of accessions within tomato wild species,Solanum pimpinellifolium to late blight

Late blight (LB), caused by the oomycete Phytophthora infestans, is one of the most devastating diseases of the cultivated tomato (Solanum lycopersicum) worldwide. Most commercial cultivars of tomato are susceptible to LB. Previously, three major LB resistance genes (Ph‐1, Ph‐2, Ph‐3) were identified and incorporated into a few commercial cultivars of tomato. Reduced effectiveness and potential breakdown of the resistance genes has necessitated identification, characterization and utilization of new sources of resistance. We evaluated the response of 67 accessions of the wild tomato species, S. pimpinellifolium to LB, under multiple field and greenhouse (GH) conditions and compared them with six control genotypes. Sixteen accessions were identified with strong LB resistance in both field and GH experiments. However, 12 accessions exhibited resistance similar to a control line which was homozygous for Ph‐2 + Ph‐3. Genotyping accessions with molecular markers for Ph‐2 and Ph‐3 were not conclusive, indicating that resistance in these accessions could be due to these or other resistance genes. Strong correlations were observed between field and GH disease response and between foliar and stem infection.     

Identifying lettuce species (Lactuca subsect. Lactuca, Asteraceae): A practical application of flow cytometry

The wild lettuce species L. serriola, L. saligna, and L. virosa are important genitors in lettuce (L. sativa) breeding. Identifying these wild species can be problematic because in some cases they look very similar. Flow cytometry was tested for its reliability and general applicability as a tool to distinguish them. Three series of tests were conducted: (1) Tests with three accessions of L. sativa and one accession of each of the wild species, repeated three times throughout the year. In each repeat, the mean relative DNA amount of L. serriola was significantly higher than that of L. saligna, but significantly lower than that of L. virosa. The mean relative DNA amount of L. sativa did not differ from that of L. serriola.(2) Tests with each wild species represented by 10 accessions. Significant differences between the accessions within each species demonstrated the presence of intraspecific variation. Notwithstanding this intraspecific variation, the relative DNA amounts of all accessions of L. serriola were significantly higher than that of all L. saligna accessions, and significantly lower than that of all L. virosa accessions. Therefore, all accessions could be assigned to the appropriate species on the basis of their DNA amounts. (3) Tests with single plants from 10 accessions of each of the wild species. These test revealed that individual plants of L. serriola, L. saligna, and L. virosa can be reliably identified with flow cytometry, when aL. serriola sample of established identity is used as internal reference. This revised version was published online in July 2006 with corrections to the Cover Date.