Relative susceptibility of different male-sterile cytoplasms in sorghum to shoot fly, <Emphasis Type="Italic">Atherigona soccata</Emphasis>

Summary The shoot fly, Atherigona soccata is an important pest of sorghum, and host plant resistance is one of the most effective components for managing this pest. Most of the hybrids grown in India based on milo cytoplasm (A₁ cytoplasm) are highly susceptible to shoot fly. Therefore, the present studies were undertaken to evaluate different male-sterile cytoplasms (CMS) for their relative susceptibility to sorghum shoot fly. Oviposition and deadheart formation were significantly lower on the maintainer lines as compared to the corresponding male-sterile lines. Among the cytoplasms tested, A₄M cytoplasm showed antixenosis for oviposition and suffered lower deadheart formation than the other cytoplasms tested. The A₄G₁ and A₄M cytoplasms suffered lower deadhearts in tillers than the other cytoplasms. Recovery following shoot fly damage in A₄M, A₃, and A₂ cytoplasms was better than in the other cytoplasms tested. The larval and pupal periods were longer and male and female pupal weights lower in A₄M and A₄VzM CMS backgrounds compared to the other CMS systems. Fecundity and antibiosis indices on CMS lines were lower than on the B-lines. The A₄M cytoplasm was found to be relatively resistant to sorghum shoot fly, and can be exploited for developing shoot fly-resistant hybrids for sustainable crop production in future.     

Wild relatives of sorghum as sources of resistance to sorghum shoot fly, Atherigona soccata

The levels of resistance to shoot fly, Atherigona soccata in sorghum germplasm are low to moderate and therefore, we evaluated 17 wild relatives of sorghum under field and greenhouse conditions as an alternate source of genes for resistance to this pest. Thirty-two accessions belonging to Parasorghum , Stiposorghum and Heterosorghum did not suffer any shoot fly damage under multi-choice conditions in the field, while one accession each of Heterosorghum ( Sorghum laxiflorum ) and Chaetosorghum ( S. macrospermum ) suffered very low shoot fly damage. Accessions belonging to S. exstans (TRC 243601), S. stipoideum (TRC 243399) and S. matarankense (TRC 243576) showed absolute non-preference for oviposition under no-choice conditions. Accessions belonging to Heterosorghum , Parasorghum and Stiposorghum were preferred for oviposition, but suffered low deadheart formation. Manual infestation of seedlings with shoot fly eggs did not result in deadheart formation in some of the accessions belonging to S. exstans (TRC 243601), S. stipoideum (TRC 243399), S. matarankense (TRC 243576) and S. purpureosericeum (IS 18944). Larval mortality was recorded in main stems of the Parasorghums . Within section Sorghum , accessions belonging to S. bicolor ssp. verticilliflorum were highly susceptible to shoot fly, as were those of S. halepense . However, a few accessions such as IS 18226 (race arundinaceum ) and IS 14212 ( S. halepense ) resulted in reduced survival and fecundity. Wild relatives of sorghum exhibited very high levels of antibiosis to A. soccata , while only low levels of antibiosis have been observed in the cultivated germplasm. Therefore, wild relatives with different mechanisms of resistance can be used as a source of alternate genes to increase the levels and diversify the basis of resistance to shoot fly, A. soccata .     

Stability of biochemical constituents and their relationships with resistance to shoot fly, Atherigona soccata (Rondani) in seedling sorghum

The stability of biochemical constituents and their association with resistance to shoot fly (Atherigona soccata Rondani) was evaluated for reducing sugars, total sugars, nitrogen, phosphorus, potassium, chlorophyll and moisture contents at weekly intervals of seedling growth (7, 14, 21 and 28 days after emergence) in 14 selected grain sorghum genotypes [five resistant accessions (IS nos. 1054, 2146, 2312, 3962 and 4664); three susceptible checks (CK 60B, CSV 1 and CSH 1); one national variety (CSV 8R); and five post-rainy advanced generation (F₆) breeding lines (148 × CS 3541, SPV 103 × IS 4664, CSV 8R × SPV 104, SPV 104 × M 35-1, and PD 3-1-11 derivative)]. The genotypes IS 2312 and IS 4664 showed stability of antixenosis for oviposition during post-rainy season advanced generation lines compared to the susceptible checks. Deadheart formation was low and the expression of resistance was stable across different seedling growth stages in IS 1054 and IS 2146. Depletion in levels of reducing sugars and phosphorus in resistant genotypes played a significant role in deadheart formation in the test genotypes. Positive association of nitrogen and potassium with oviposition at early seedling stages indicated their role in releasing chemical cues for oviposition. Low levels of reducing sugars and total sugars seemed to enhance the degree of resistance to sorghum shoot fly. The total chlorophyll content had no relationship with antixenosis for oviposition. No relationship was observed between moisture content of sorghum seedlings and shoot fly resistance. Low concentrations of reducing sugars, total sugars, nitrogen, phosphorus and potassium in sorghum seedlings greatly enhanced the degree of antixenosis for oviposition/feeding and deadheart formation, and can be used as selection criteria for resistance to shoot fly.     

Pattern of genetic inheritance of morphological and agronomic traits of sorghum associated with resistance to sorghum shoot fly, <Emphasis Type="Italic">Atherigona soccata</Emphasis>

Sorghum shoot fly, Atherigona soccata is an important pest of sorghum during the seedling stage, which influences both fodder and grain yield. To understand the nature of inheritance of shoot fly resistance in sorghum, we performed generation mean analysis using two crosses IS 18551 × Swarna and M 35-1 × ICSV 700 during the 2013–2014 cropping seasons. The F₁, F₂, BC₁ and BC₂ progenies, along with the parental lines were evaluated for agronomic and morphological traits associated with resistance/susceptibility to sorghum shoot fly, A. soccata. The cross IS 18551 × Swarna exhibited significant differences between the parents for shoot fly deadhearts (%) in the postrainy season. The progenies of this cross exhibited lower shoot fly damage, suggesting that at least one of the parents should have genes for resistance to develop shoot fly-resistant hybrids. Leaf glossiness, leafsheath pigmentation and plant vigor score during the seedling stage exhibited non-allelic gene interactions with dominant gene action, whereas 100 seed weight showed both additive and dominant gene interactions. Presence of awns showed recessive nature of the awned gene. Generation mean analysis suggested that both additive and dominance gene effects were important for most of the traits evaluated in this study, but dominance had a more pronounced effect.     

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.     

Resynthesizing <Emphasis Type="Italic">Brassica napus</Emphasis> from interspecific hybridization between <Emphasis Type="Italic">Brassica rapa</Emphasis> and <Emphasis Type="Italic">B. oleracea</Emphasis> through ovary culture

Using three varieties of Brassica rapa, cv. Hauarad (accession 708), cv. Maoshan-3 (714) and cv. Youbai (715), as the maternal plants and one variety of B. oleracea cv. Jingfeng-1 (6012) as the paternal plant, crosses were made to produce interspecific hybrids through ovary culture techniques. A better response of seed formation was observed when ovaries were cultured in vitro at 9–12 days after pollination on the basal MS and B5 media supplemented with 6-benzylaminopurine (BA) and naphthylacetic acid (NAA). The best response was observed for cross 714×6012 with the rate of seeds per ovary reaching 43.0%. Seeds for cross 715×6012 showed the best germination response (66.7%) on the regeneration medium (MS+1.0 mg l^–1 BA+0.05 mg l^–1 NAA). In all three cross combinations, good response in terms of root number and length of plants was observed on the root induction medium (MS+1.0 mg l^–1 BA+0.1 mg l^–1 NAA). A better response was observed for the regenerated plants cultured for 14 days than for 7 days. The ovary-derived plants with well-developed root system were hardened for 8 days and their survival rate reached over 80%. Cytological studies showed that the chromosome number of all plants tested was 19 (the sum of both parents), indicating that these regenerated plants were all true hybrids of B. rapa (n = 10) × B. oleracea (n = 9). The regenerated plants were doubled with colchicine treatment, and the best response in the crosses 708×6012, 714×6012 and 715×6012 was observed when treated with 170 mg l^–1 colchicine for up to 30 h and their doubling frequency reached 52, 56 and 62%, respectively.     

Mechanisms and diversity of resistance to sorghum shoot fly,Atherigona soccata

Sorghum shoot fly, Atherigona soccata, is one of the important pests of postrainy season sorghums. Of the 90 sorghum genotypes evaluated for resistance to this pest, RHRB 12, ICSV 713, 25026, 93046 and 25027, IS 33844‐5, Giddi Maldandi and RVRT 3 exhibited resistance in postrainy season, while ICSB 463, Phule Anuradha, RHRB 19, Parbhani Moti, ICSV 705, PS 35805, IS 5480, 5622, 17726, 18368 and 34722, RVRT 1, ICSR 93031 and Dagidi Solapur showed resistance in rainy season, suggesting season‐specific expression of resistance to A. soccata. ICSB 461, ICSB 463, Phule Yasodha, M 35‐1, ICSV 700, 711, 25010, 25019 and 93089, IS 18662, Phule Vasudha, IS 18551 and 33844‐5 and Barsizoot had fewer deadhearts than plants with eggs across seasons, suggesting antibiosis as one of the resistance mechanism. Five genotypes exhibited resistance with high grain yield across seasons. Correlation, path and stepwise regression analyses indicated that leaf glossiness, seedling vigour, trichome density, oviposition and leaf sheath pigmentation were associated with the expression of resistance/susceptibility to shoot fly, and these can be used as marker traits to select and develop shoot fly‐resistant sorghums.     

Genetics of resistance to <Emphasis Type="Italic">Cucumber mosaic virus</Emphasis> in <Emphasis Type="Italic">Cucumis sativus</Emphasis> var. <Emphasis Type="Italic">hardwickii</Emphasis> R. Alef

The genetics of resistance to Cucumber mosaic virus (CMV) in Cucumis sativus var. hardwickii R. Alef, the wild progenitor of cultivated cucumber was assessed by challenge inoculation and by natural infection of CMV. Among the 31 genotypes of C. sativus var. hardwickii collected from 21 locations in India the lowest mean percent disease intensity (PDI) was recorded in IC-277048 (6.33%) while the highest PDI was observed in IC-331631 (75.33%). All the four cultivated varieties (DC-1, DC-2, CHC-1 and CHC-2) showed very high PDI and susceptible disease reaction. Based on mean PDI, 8 genotypes were categorized as resistant, 13 as moderately resistant, 9 as moderately susceptible and one as susceptible. A chi-square test of frequency distribution based on mean PDI in F₂ progenies of six resistant × susceptible crosses revealed monogenic recessive Mendelian ratio 1(R):3(S) to be the best fit. This monogenic recessive model was further confirmed by 1(R):1(S) ratio as the best fit for back cross with resistant parent and no fit for either 3:1 or 1:1 in the back cross with the susceptible parent. The results revealed that CMV resistance in C. sativus var. hardwickii was controlled by a single recessive gene. Considering the cross compatibility between C. sativus var. hardwickii and cultivated cucumber, the resistance trait can be easily transferred to cultivated species through simple backcross breeding.     

CO<Subscript>2</Subscript>-assimilation and chlorophyll fluorescence as indirect selection criteria for host tolerance against <Emphasis Type="Italic">Striga</Emphasis>

Striga hermonthica (Del.) Benth. is a parasitic weed on tropical cereals causing serious yield losses in Africa. The use of host crop varieties with improved resistance and tolerance against this parasite is a key component of an integrated control strategy. Breeding for tolerance is however seriously hampered by the absence of reliable and yet practical selection measures. The observation that the photosynthetic rate of tolerant genotypes is less sensitive to Striga infection was used as a starting point to search for suitable selection measures. In a greenhouse pot experiment the effect of Striga infection on the photosynthesis of four sorghum (Sorghum bicolor [L.] Moench) genotypes, differing in Striga tolerance level, was measured at three moments in time (26, 48 and 75 days after sowing). Genotypes were CK60-B, E36-1, Framida and Tiémarifing. Measurements involved CO₂-assimilation (A) and three chlorophyll fluorescence characteristics (electron transport rate through photosystem II [ETR], photochemical [Pq] and non-photochemical quenching [NPq]). Striga infection negatively affected A, ETR and Pq. Based on A and Pq, genotypes with superior levels of tolerance (Tiémarifing) could be discriminated from genotypes with superior level of resistance (Framida). Both A and Pq showed high heritabilities and consequently clear and predictable differences between genotypes. Using discriminative ability, heritability and cost effectiveness as main criteria, photochemical quenching (Pq) was concluded to possess the highest potential to serve as indirect selection measure for host plant tolerance to Striga. Screening should preferably be conducted at relatively high Striga infestation levels, between Striga emergence and host plant flowering.     

Genetic Divergence and Molecular Characterization of Sorghum Hybrids and their Parents for Reaction to Atherigona Soccata (Rondani)

Summary Simple sequence repeat (SSR) markers linked to quantitative trait loci (QTL) associated with resistance to sorghum shoot fly, Atherigona soccata resistance were used to characterize the genetic and phenotypic diversity of 12 cytoplasmic male-sterile (CMS) and maintainers, 12 restorer lines, and 144 F₁ hybrids. The genetic diversity was quite high among the shoot fly-susceptible parents and the hybrids based on them, as indicated by high polymorphic information content (PIC) values, while limited genetic diversity was observed among shoot fly-resistant lines. The phenotypic and genotypic dissimilarity analysis indicated that the shoot fly-resistant and -susceptible parents were 73.2 and 38.5% distinct from each other, and the morphological and genetic distances of certain resistant and susceptible cross combinations was more than their resistant or susceptible parents. Genetic variability among the groups was low (10.8%), but high within groups (89.2%). The genetic and morphological distances suggested that the F₁ hybrids were closer to CMS (5 to 12% dissimilar) than the restorer (11 to 87% dissimilar), suggesting that CMS influences the expression of resistance to sorghum shoot fly. The SSR markers can be used to characterize the homologous traits in sorghum germplasm.     

<Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation of faba bean <Emphasis Type="Italic">(Vicia faba</Emphasis> L.) using embryo axes

A system for the production of transgenic faba bean by Agrobacterium-mediated transformation was developed. This system is based upon direct shoot organogenesis after transformation of meristematic cells derived from embryo axes. Explants were co-cultivated with A. tumefaciens strain EHA105/pGlsfa, which harbored a binary vector containing a gene encoding a sulphur rich sunflower albumin (SFA8) linked to the bar gene. Strain EHA 101/pAN109 carrying the binary plasmid containing the coding sequence of a mutant aspartate kinase gene (lysC) from E. coli in combination with neomycinphosphotransferase II gene (nptII) was used as well. The coding sequences of SFA8 and LysC genes were fused to seed specific promoters, either Vicia faba legumin B4 promoter (LeB4) or phaseolin promoter, respectively. Seven phosphinothricin (PPT) resistant clones from Mythos and Albatross cultivars were recovered. Integration, inheritance and expression of the transgenes were confirmed by Southern blot, PCR, enzyme activity assay and Western blot.     

Production and characterization of inter-sectional hybrids between <Emphasis Type="Italic">Kalanchoe spathulata</Emphasis> and <Emphasis Type="Italic">K. laxiflora</Emphasis> ( = <Emphasis Type="Italic">Bryophyllum crenatum</Emphasis>)

The genus Kalanchoe is currently divided into section Kalanchoe and section Bryophyllum, and there has been no successful report on the production of inter-sectional hybrids. Therefore, reciprocal crosses were made between Kalanchoe spathulata (sect. Kalanchoe) and K. laxiflora (sect. Bryophyllum) in order to obtain basic information on the reproductive barriers between these two sections. The seeds were aseptically germinated in vitro and the plants were grown in greenhouse till flowering. When K. spathulata was used as a maternal donor, 39 out of 80 plants showed intermediate characteristics between K. spathulata and K. laxiflora. In contrast, no plants were obtained in the reverse crosses. Hybridity of these plants was confirmed by flow cytometric analysis, chromosome numbers and RAPD analysis. Bulbil formation on the leaf margin as one of the conspicuous characteristics of K. laxiflora was not observed in the hybrids. Some of the hybrid lines showed some pollen fertility, but failed to yield viable seeds by self-pollination or backcross-pollination. Successful production of the inter-sectional hybrid between the two species suggests that they are not so distantly related as considered previously.     

Identification of RAPD markers linked to the rust (<Emphasis Type="Italic">Uromyces fabae</Emphasis>) resistance gene in pea (<Emphasis Type="Italic">Pisum sativum</Emphasis>)

Summary Two RAPD markers linked to gene for resistance (assayed as pustule number cm⁻² leaf area) to rust [Uromyces fabae (Pers.) de Bary] in pea (Pisum sativum L.) were identified using a mapping population of 31 BC₁F₁ [HUVP 1 (HUVP 1 × FC 1] plants, FC 1 being the resistant parent. The analysis of genetics of rust resistance was based on the parents, F₁, F₂, BC₁F₁ and BC₁F₂ generations. Rust resistance in pea is of non-hypersensitive type; it appeared to be governed by a single partially dominant gene for which symbol Ruf is proposed. Further, this trait seems to be affected by some polygenes in addition to the proposed oligogene Ruf. A total of 614 decamer primers were used to survey the parental polymorphism with regard to DNA amplification by polymerase chain reaction. The primers that amplified polymorphic bands present in the resistant parent (FC 1) were used for bulked segregant analysis. Those markers that amplified consistently and differentially in the resistant and susceptible bulks were separately tested with the 31 BC₁F₁ individuals. Two RAPD makers, viz., SC10-82₃₆₀ (primer, GCCGTGAAGT), and SCRI-71₁₀₀₀ (primer, GTGGCGTAGT), flanking the rust resistance gene (Ruf) with a distance of 10.8 cM (0.097 rF and LOD of 5.05) and 24.5 cM (0.194 rF and a LOD of 2.72), respectively, were identified. These RAPD markers were not close enough to Ruf to allow a dependable maker-assisted selection for rust resistance. However, if the two makers flanking Ruf were used together, the effectiveness of MAS would be improved considerably.     

A simple,rapid and reliable bioassay for evaluating seedling vigor under submergence in <Emphasis Type="Italic">indica</Emphasis> and <Emphasis Type="Italic">japonica</Emphasis> rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Submergence is a major stress causing yield losses particularly in the direct-seeded rice cultivation system and necessitates the development of a simple, rapid and reliable bioassay for a large scale screening of rice germplasms with tolerance against submergence stress. We developed two new bioassay methods that were based primarily on the seedling vigor evaluated by the ability of fast shoot elongation under submerged conditions, and compared their effectiveness with two other available methods. All four bioassay methods using cultivars of 7 indica and 6 japonica types revealed significant and consistent cultivar differences in seedling vigor under submergence and/or submergence tolerance. Japonica cultivars were more vigorous than indica cultivars, with Nipponbare being the most vigorous. The simplest test tube method showed the highest correlations to all other methods. Our results suggest that seedling vigor serves as a submergence avoidance mechanism and confers tolerance on rice seedlings to flooding during early crop establishment. A possible relationship is discussed between seedling vigor based on fast shoot elongation and submergence tolerance defined by recovery from submergence stress.     

Molecular markers linked to <Emphasis Type="Italic">Bn</Emphasis>;<Emphasis Type="Italic">rf</Emphasis>: a recessive epistatic inhibitor gene of recessive genic male sterility in <Emphasis Type="Italic">Brassica napus </Emphasis>L.

7–7365AB is a recessive genic male sterile (RGMS) two-type line, which can be applied in a three-line system with the interim-maintainer, 7–7365C. Fertility of this system is controlled by two duplicate dominant epistatic genes (Bn;Ms3 and Bn;Ms4) and one recessive epistatic inhibitor gene (Bn;rf). Therefore an individual with the genotype of Bn;ms3ms3ms4ms4Rf_ exhibits male sterility, whereas, plant with Bn;ms3ms3ms4ms4rfrf shows fertility because homozygosity at the Bn;rf locus (Bn;rfrf) can inhibit the expression of two recessive male sterile genes in homozygous Bn;ms3ms3ms4ms4 plant. A cross of 7–7365A (Bn;ms3ms3ms4ms4RfRf) and 7–7365C (Bn;ms3ms3ms4ms4rfrf) can generate a complete male sterile population served as a mother line with restorer in alternative strips for the multiplication of hybrid seeds. In the present study, molecular mapping of the Bn;Rf gene was performed in a BC₁ population from the cross between 7–7365A and 7–7365C. Bulked segregant analysis (BSA) and amplified fragment length polymorphism (AFLP) technique was used to identify molecular markers linked to the gene of interest. From a survey of 768 primer combinations, seven AFLP markers were identified. The closest marker, XM5, was co-segregated with the Bn;Rf locus and successfully converted into a sequence characterized amplified region (SCAR) marker, designated as XSC5. Two flanking markers, XM3 and XM2, were 0.6 cM and 2.6 cM away from the target gene, respectively. XM1 was subsequently mapped on linkage group N7 using a doubled-haploid (DH) mapping population derived from the cross Tapidor × Ningyou7, available at IMSORB, UK. To further confirm the location of the Bn;Rf gene, additional simple sequence repeat (SSR) markers in linkage group N7 from the reference maps were screened in the BC₁ population. Two SSR markers, CB10594 and BRMS018, showed polymorphisms in our mapping population. The molecular markers found in the present study will facilitate the selection of interim-maintainer.     

Identification of levels of resistance to cassava root rot disease (<Emphasis Type="Italic">Botryodiplodia theobromae</Emphasis>) in African landraces and improved germplasm using <Emphasis Type="Italic">in vitro</Emphasis> inoculation method

Cassava root rot disease is an increasing problem in Africa where yield losses of about 80% have been recorded. We evaluated 290 African landraces and 306 improved genotypes from the germplasm collections of the International Institute of Tropical Agriculture (IITA), for sources of resistance using root slice laboratory assay. Disease severity was assessed quantitatively by direct percentage estimation (PS) and by use of a rating scale (RS). Both methods of assessment were compared for identification of variability in the germplasm, and genotypes were classified into response groups using an enlarged rank-sum method that combined the PS and RS assessments. The two scoring methods revealed continuous variation (P < 0.001) for resistance in the sets of germplasm. Disease assessments based on PS and RS were highly correlated in both the improved germplasm (r = 0.75) and the landraces (r = 0.72). Based on PS assessment, 50 improved genotypes (16.3%) and 53 landraces (18.3%) showed significantly lower disease scores than the resistant control. The rank-sum method separated each set of collections into highly resistant, resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible groups. Fifty-nine improved genotypes (16.4%) and 61 African landraces (16.9%) were identified as either highly resistant or resistant. Generally, these genotypes exhibited resistance by limiting the growth of the pathogen (reduced amount of invaded surface area). This type of rate-reducing resistance is highly heritable and a quantitative trait which can be harnessed in breeding. Genotypes subsets were identified for further studies into the genetic basis of resistance to root rot disease.     

Ploidy level studies on the <Emphasis Type="Italic">Dioscorea cayenensis</Emphasis>/<Emphasis Type="Italic">Dioscorea rotundata</Emphasis> complex core set

The Guinea yams, Dioscorea cayenensis Lam. and D. rotundata Poir. (D. cayenensis–D. rotundata complex), represent a highly important crop, widely distributed in the humid and semi-humid tropics. The ploidy levels of 170 accessions of the core set of Guinea yams from West African countries was determined using flow cytometry with propidium iodide staining. One hundred and eight of the genotypes were found to be tetraploid, 47 were hexaploid and five were octoploid. One mixoploid individual containing tetraploid and hexaploid nuclei was also detected. A deeper analysis considering each separate taxon revealed that while for D. rotundata the majority of individuals were tetraploid, for D. cayenensis this ploidy level was not detected in any of the accessions. Also, no association between ploidy level and place of cultivation was found for the evaluated germplasm. The obtained data is highly valuable for breeding programs of Guinea yam, especially for the optimization of future hybridization experiments directed to the genetic improvement of this economically important crop.     

Characterization of the resistance to <Emphasis Type="Italic">Phytophthora infestans</Emphasis> in local potato cultivars in Bolivia

This experiment was carried out to investigate whether and how much field resistance to late blight, caused by Phytophthora infestans, is present in the local cultivated potato germplasm. In total 36 entries were compared in a field experiment in an area highly conducive to late blight development. Of the 36 cultivars 32 were local cultivars belonging to five Solanum species, S. tuberosum (1 accession), S. andigena (18), S. juzepczukii (2), S. stenotomum (9) and S. ajanhuiri (2). The other four cultivars were derived from breeding programmes, one being the Dutch cultivar Alpha used as a highly susceptible control. The 36 cultivars were planted according to a simple 6 × 6 lattice design with three replicates. Each replicate was divided in six incomplete blocks each with six cultivars. The disease severity was assessed weekly during 9 weeks starting 48 days after planting. The area under the disease progress curve (AUDPC) was used as a measure of the field resistance. Nine isolates from surrounding potato fields were tested for their virulence to the resistance genes R1–R11 using 22 differential cultivars. The components of the field resistance of 19 of these cultivars were compared in the greenhouse using a local isolate with virulence to all known R-genes, except to R9. The nine isolates represented seven races with a race complexity varying from 7 to 10 virulence factors. All isolates carried virulence against R1, R2, R3, R7, R10 and R11, while virulence against R9 was absent. The AUDPC among the 32 local cultivars ranged from very large, significantly larger than that of ‘Alpha’ to very small. The AUDPC from S. stenotomum accessions ranged from very large to intermediate, those from S. andigena accessions from large to very small. Especially among the S. andigena accessions interesting levels of field resistance were found. Four components of field resistance were assessed, latency period (LP), lesion size (LS), lesion growth rate (LGR) and relative sporulation area (RSA). All four showed a considerable variation among the cultivars. The LP ranged from 3½ to 6 days. The LS ranged from 225 mm² to 20 mm². The LGR varied about six-fold, the RSA more than 10-fold. The components tended to vary in association with one another. LP and LGR were well associated with each other and had a significant correlation with the AUDPC.     

A cytoplasmic-nuclear male-sterility system derived from a cross between <Emphasis Type="Italic">Cajanus cajanifolius</Emphasis> and <Emphasis Type="Italic">Cajanus cajan</Emphasis>

Cytoplasmic-nuclear male-sterility is an important biological tool, which has been used by plant breeders to increase yields in cross-pollinated cereals and vegetables by commercial exploitation of the phenomenon of hybrid vigor. In legumes, no such example exists due to the absence of an economic way of mass pollen transfer from male to female parent. Pigeonpea [Cajanus cajan (L.) Millsp.], however, is a different legume where a moderate level of insect-aided natural out-crossing (25–70%) exists and it can be used to produce commercial hybrid cultivars, if an efficient and stable cytoplasmic-nuclear male-sterility (CMS) system is available. This paper reports the development of a stable CMS system (ICP 2039A), derived from an inter-specific hybrid of Cajanus cajanifolius, a wild relative of pigeonpea, with a cultivar ICP 11501. Using this genetic material, designated as the A₄ cytoplasm, a number of fertility restorers and maintainers have been developed. The best short-duration experimental pigeonpea hybrid ICPH 2470 produced 3205 kg ha⁻¹ grain yield in 125 days, exhibiting 77.5% advantage over the control cultivar UPAS 120. At present, all the important biological systems necessary for a successful commercial hybrid breeding program are available in pigeonpea and the package of this technology has been adopted by private seed sector in India for the production and marketing of hybrid varieties.     

Production of intergeneric hybrid plants between <Emphasis Type="Italic">Sandersonia aurantiaca</Emphasis> and <Emphasis Type="Italic">Gloriosa rothschildiana</Emphasis> via ovule culture (Colchicaceae)

Intergeneric hybrid plants between Colchicaceous ornamental plants, Sandersonia aurantiaca and Gloriosa rothschildiana, have successfully been produced via ovule culture. After 5 days of reciprocal cross-pollination, a few pollen tubes were observed in the ovary. Although seeds were obtained in both reciprocal cross-combinations, they did not germinate under ex vitro conditions. Ovules with placental tissues isolated 14 days after cross-pollination of S. aurantiaca × G. rothschildiana were cultured on a medium containing 0.01 mg l^–1 each of -naphthaleneacetic acid (NAA) and 6-benzyladenine (BA), on which 41.5% of ovules swollen and produced callus-like structures within 10 weeks. When such swollen ovules were transferred to a medium containing 0.1 mg l^–1 each of NAA and BA, 7.5% of the initially cultured ovules produced rhizome-like structures within 6 weeks. Among the rhizome-like structures, those derived from two independent ovules (3.7% of the initially cultured ovules) produced multiple shoots following transfer to a medium containing 0.25 mg l^–1 NAA and 2.5 mg l^–1 BA. Multiple shoot-derived plantlets were established on a plant growth regulator-free medium, and they were successfully transplanted to pots. Early verification of their hybridity was accomplished by flow cytometry (FCM) analysis, chromosome observation and rDNA analysis.