Genetic resistance to root-knot nematode (Meloidogyne javanica) in eggplant (Solanum melongena)

A germplasm collection of 39 eggplant Solanum melongena genotypes and one accession of S. torvum was evaluated for resistance to the root-knot nematode (Meloidogyne javanica) by using controlled greenhouse tests. Different degrees of resistance to the disease caused by this nematode species were observed among the genotypes tested. Complete resistance (no nematode egg mass formation up to 7 weeks after inoculation) was detected in one accession belonging to domesticated S. melongena species. Good levels of incomplete resistance were also observed in some commercial eggplant genotypes. This is apparently the first report of a source of complete resistance to M. javanica within the S. melongena gene pool and our finding could greatly facilitate the incorporation of this trait into commercial eggplant cultivars. S. torvum, previously described as resistant to several root-knot nematode species (including M. javanica, M. arenaria, and M. incognita) was also confirmed as a source of resistance to this Brazilian population of M. javanica. Therefore, S. torvum can be considered as one of the most promising sources of broad-spectrum resistance genes against root-knot nematodes. Broad-spectrum resistance is of paramount importance for breeding programmes focused on the development of cultivars for tropical and subtropical areas of the world where multiple infestation of soils with distinct Meloidogyne species is a very common feature.     

Transfer of resistance to Verticillium dahliae Kleb. from Solanum torvum S.W. into potato (Solanum tuberosum L.) by protoplast electrofusion

Summary Interspecific somatic hybrid plants were regenerated after electrofusion of mesophyll protoplasts with the objective of transferring resistance to Verticillium dahliae from Solanum torvum into potato. Early selection of the putative hybrids was based on differences in cultural behaviour of the parental and hybrid calli (particularly the ability of the latter to regenerate early) in combination with morphological markers. Four putative hybrids were recovered from hundreds of calli, probably resulting from complementation of the two parental genomes. The regenerates were tetraploids (2n=4×=48 chromosomes) and exhibited intermediate traits including leaf form, plant morphology and the presence of anthocyanin. The hybrid nature of the four selected plants was confirmed by examining isoenzyme patterns for isocitrate dehydrogenase (Idh), malate dehydrogenase (Mdh), phosphoglucoisomerase (Pgi) and 6-phosphogluconate dehydrogenase (6-Pgd). While the hybrid plants rooted readily and grew vigorously under in vitro conditions, in the greenhouse their development and growth were retarded by difficulties in rooting. When grafted on potato or S. torvum rootstocks, the hybrid plants recovered normal development and growth. Again, they exhibited intermediate morphological traits. Tests for resistance realized in vitro with medium containing 50% Verticillium wilt filtrate showed that all the somatic hybrids were resistant to the fungus filtrate.     

Failure in an interspecific cross between Solanum khasianum Clarke and Solanum mammosum L.

Summary Attempts to obtain a successful interspecific cross between Solanum khasianum Clarke and Solanum mammosum L. were unsuccessful, and the probable reasons for this failure were investigated. A reduced number of viable pollen grains and low receptivity of the stigmas of S. mammosum L. and heterostyly in both species are the probable reasons for the failure of the attempted interspecific crosses between S. khasianum Clarke and S. mammosum L.     

Crossability and cytological studies in Solanum macrocarpon and Solanum linnaeanum (Solanaceae).

Summary Crossing experiments involving the various groups of Solanum macrocarpon L. complex, including wild (dasyphyllum), semi-wild and cultivars produced fully fertile F1 and F2 hybrids. This confirmed earlier findings that these groups belong to the same biological species. S. macrocarpon complex and S. linnaeanum Hepper ex Jaeger are isolated by reproductive barriers. F1 and F2 hybrids between various groups of S. macrocarpon showed heterosis. F2 superior hybrids were isolated as candidates for the future breeding programmes. Most wild-type traits like prickliness, hairiness were dominant to those possessed by cultivars. Relatively resistant hybrids to pest attack were noted. S. macrocarpon complex and S. linnaeanum are diploids (2n=24). The overall nature of the karyotype suggests that the two are related. The F1 hybrids between the cultivars of S. macrocarpon and the wild group (S. dasyphyllum) showed normal meiosis. A lack of isolating barriers confirmed that S. macrocarpon complex constitute a single biological species.     

Heritability of resistance to foliar late blight in a diploid hybrid potato population of Solanum phureja×Solanum stenotomum

The emergence of new races of Phytophthora infestans has necessitated the search for additional sources of potato germplasm with resistance to late blight. This study examined 281 clones, derived from 72 families of a diploid random-mated hybrid population of Solanum phureja×Solanum stenotomum. The clones were evaluated in a replicated field trial for 2 years with the control cultivar ‘Atlantic’ in Pennsylvania, USA. The P. infestans US-8 A2 mating type culture was used to inoculate spreader rows of susceptible S. tuberosum cv.‘Russet Burbank’. Percent defoliation caused by the late blight fungus was estimated visually in each plot three times near the end of the growing season. Area under the disease progress curve (AUDPC) was estimated and showed that late blight was more severe in 1997 than in 1996. Genetic differences among clones and significant, but small, clone–environment interaction were detected for AUDPC. Broad-sense and narrow-sense heritability estimates, over years, were 0.79 ± 0.05 (P = 0.05) and 0.78 ± 0.29, respectively. Seventy-five percent of the diploid clones had a significantly lower mean AUDPC than Atlantic. These results support the idea that this diploid population is worthy of use in breeding for late blight resistance in tetraploid potato cultivars.     

Segregation of isozymes in selfed progenies of a synthetic amphidiploid between Solanum integrifolium and S. melongena

Isozyme and cytogenetic analyses were performed on selfed progenies of a synthetic amphidiploid between scarlet eggplant, Solanum integrifolium (= S. aethiopicum),and eggplant, Solanum melongena `DMP', for estimating genetic uniformity. Isozymes in the 379 examined seedlings segregated into five genotypes (phenotypes) each at the four loci examined, Pgd-2 of phosphogluconate dehydrogenase (E.C.1.1.1.43), Idh-2 of isocitrate dehydrogenase (E.C.1.1.1.41), Pgm-2 of phosphoglucomutase (E.C.2.7.5.1)and Skdh-1 of shikimate dehydrogenase (E.C.1.1.1.25), indicating that the selfed seedlings were not genetically uniform. Most of the examined 15 selfed seedlings exhibited a somatic chromosome number of 48, that is the same number of the synthetic amphidiploid, whereas isozyme genotypes among them were variable. It is suggested that the segregation of isozymes was not caused by variation of chromosome number but by genetic segregation of isozyme genes. The genome of the synthetic amphidiploid was indicated to be unstable. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tolerance to low temperatures and tuber soft rot in hybrids between Solanum commersonii and Solanum tuberosum obtained through manipulation of ploidy and endosperm balance number (EBN)

The objectives of this study were to evaluate the tolerance to low temperatures and tuber soft rot in hybrids between Solanum commersonii and Solanum tuberosum. The experimental materials consisted of F₁ triploid, BC₁ pentaploid‐near pentaploid and BC₂ tetraploid–near tetraploid hybrids. The F₁ triploids had a freezing tolerance and acclimatization capacity closest to S. commersonii. This indicated that the endosperm barriers which prevent the introgression of 1EBN S. commersonii into 4EBN S. tuberosum had been overcome. Indeed, the triploids produced 2n eggs, thus giving a compatible maternal to paternal EBN ratio in the hybrid endosperm generated by the 3x(2EBN) × 4x(3EBN) crosses. The tolerance to low temperatures of BC₁ and BC₂ hybrids was lower than that of the F₁. However, a number of genotypes were identified which were able to withstand temperatures down to ‐5°C. Some BC₂ hybrids were also tested for their tolerance to tuber soft rot, and some resistant hybrids were detected. A number of them combined the capacity for cold acclimatization with tolerance to tuber soft rot. These hybrids have an EBN of 4; they are fertile and have been used in backcrosses with 4EBN S. tuberosum.     

Inheritance in Solanum aethiopicum,the scarlet eggplant

Summary Analyses of F₁ and F₂ hybrid progenies from crosses between the ancestral species Solanum anguivi and cultivars of its domesticated derivative S. aethiopicum, have proved the mode of inheritance of prickles, stellate hairs and some other morphological characters and suggested the mode for several more. Most wild-type traits were dominant: many recessive domesticated traits involved imperfect morphogenesis suggesting loss of genetic control. F₁ hybrids between cultivars show marked heterosis and are recommended for crop production.     

Fertility restoration of hybrids between Solanum melongena L. and S. aethiopicum L. Gilo Group by chromosome doubling and cytoplasmic effect on pollen fertility

Reproductive fertility traits were studied in the reciprocal hybrids of the eggplant(Solanum melongena L.) and S. aethiopicum L. Gilo Group, and in synthetic amphidiploids to discover whether fertility in these reciprocal hybrids was restored by chromosome doubling. Isozyme and RAPD analyses confirmed hybridity of the hybrids and amphidiploids. Analyses of chloroplast and mitochondrial DNAs confirmed that the cytoplasm of each of the hybrids and amphidiploids was from the maternal parent. Pollen sterility of S. melongena × S. aethiopicum Gilo Group [F₁ (Mel × Aet)] was restored by chromosome doubling, while the reciprocal hybrid S. aethiopicum Gilo Group ×S. melongena [F₁ (Aet × Mel)]and its amphidiploid did not produce any pollen grains; their microspores degenerated without being released from tetrads. Hence the cytoplasm of S. aethiopicum Gilo Group seems to beresponsible for their pollen-non-formation type sterility of the hybrid. Both the F₁ hybrids did not set any fruits by either selfing or backcrossing, while their amphidiploids set fruits after pollinating with pollen from the amphidiploid of F₁ (Mel × Aet). Seeds obtained from both the amphidiploids germinated normally. Chromosome doubling has been effective in restoring fertility of the hybrids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analysis of late blight resistance in a new RIL population of tomato derived from LB-resistant Solanum pimpinellifolium accession PI 270443

Late blight (LB), caused by Phytophthora infestans, is one of the most devastating diseases of tomato (Solanum lycopersicum) worldwide. Aggressive pathogen isolates resistant to fungicides have driven research in favour of finding new sources of host resistance for tomato breeding. Recently, we reported S. pimpinellifolium accession PI 270443 exhibiting LB resistance stronger than all commercial LB-resistant tomato cultivars. The purpose of this study was to examine the inheritance of LB resistance conferred by this accession. An interspecific cross was made between PI 270443 and a LB-susceptible tomato breeding line and advanced to F₁₀ generation. A total of 166 F₉ and corresponding F₁₀ recombinant inbred lines (RILs) were evaluated for response to LB in four replicated greenhouse experiments. Estimates of heritability (h²) of LB resistance, determined by parent–offspring (F₉:F₁₀) correlation analysis, ranged from 0.66 to 0.81, with an average of 0.76. The moderately high h² of LB resistance in PI 270443 suggests the utility of this accession for tomato breeding. Molecular mapping and RNA-sequencing efforts are underway to identify genes underlying LB resistance in PI 270443.     

Resistance to viruses in F1 hybrids produced by direct crossing between diploid Solanum series Tuberosa and diploid S. brevidens (series Etuberosa) using S. phureja for rescue pollination

Resistance to potato viruses was examined in the F₁ hybrids (TET) obtained from a cross between a diploid (2n = 24), tuber-bearing interspecific hybrid 87HW13.7 (Solanum tuberosum W231 ×S. multi-dissectum PI 473354) and a diploid (2n = 24), nontuber-bearing wild potato species (S. brevidens CPC 2451) using S. phureja IvP35 (2n = 24) for rescue pollination. The parental plants were susceptible to PVX, whereas two hybrids (TET38.2 and TET38.9) and S. phureja IvP35 reacted with hypersensitivity to PVX. Two hybrids (TET 38.9 and TET 38.12) were extremely resistant to PVY°, which was similar to S. brevidens and S. phureja IvP35, whereas the remaining two hybrids were moderately resistant to PVY°. No resistance to PVA and PLRV was observed in the progenies, in contrast to S. brevidens which was extremely resistant to PVA and PLRV. Hypersensitivity to PVX in two progenies suggested (1) integration by somatic translocation or heterofertilization and expression of genes from the rescue pollinator S. phureja IvP35, or (2) transgressive or complementary gene action.     

Introgression from wild Cicer reticulatum to cultivated chickpea for productivity and disease resistance

Interspecific hybridization is known to improve productivity and resistance to diseases in many crops. Therefore, an attempt was made to introgress productivity and disease resistance into chickpea from wild Cicer species. The true F₁ hybrids of cultivated chickpea genotypes ‘L550’ and ‘FGK45’ with C. reticulatum were backcrossed twice to their cultivated female parents to minimize the linkage drag of undesirable wild traits. The pedigree method was followed to advance the segregating populations from straight crosses (without backcross) and BC₁/BC₂ generations to F₅–F₇. The interspecific derivatives recorded up to a 16.9% increase over the check cultivars and a 25.2% increase over the female parent in a preliminary yield evaluation trial. Of the 22 interspecific derivatives thus derived, four desi and two kabuli lines were further evaluated for seed yield in replicated trials at three diverse locations. These lines possess a high degree of resistance to wilt, foot rot and root rot diseases, and recorded a 6.1–17.0% seed yield increase over the best check cultivars.     

High resolution map of eggplant (Solanum melongena) reveals extensive chromosome rearrangement in domesticated members of the Solanaceae

A linkage map of eggplant was constructed for an interspecific F₂ population derived from a cross between Solanum linnaeanum MM195 and S. melongena MM738. The map contains 400 AFLP^® (amplified fragment length polymorphism), 348 RFLP (restriction fragment length polymorphism) and 116 COSII (conserved ortholog set) markers. The 864 mapped markers encompass 12 linkage groups, span 1,518 cM and are spaced at an average interval of 1.8 cM. Use of orthologous markers allowed confirmation of the established syntenic relationships between eggplant and tomato chromosomes and helped delineate the nature of the 33 chromosomal rearrangements and 11 transpositions distinguishing the two species. This genetic map provides a 2- to 3-fold improvement in marker density compared to previously published interspecific maps. Because the interspecific mapping population is rich in morphological variation, this greater genome saturation will be useful for QTL (quantitative trait locus) analyses. The recent release of the tomato genome sequence will provide additional opportunities for exploiting this map for comparative genomics and crop improvement.     

Identification of Maintainer Genes in Brassica napus L. for the Male-Sterility-Inducing Cytoplasm of Diplotaxis muralis L.

Male fertility of F¹ interspecific hybrid plants derived from crosses between cytoplasmic male-sterile Brassica campestris in Diplotaxis muralis cytoplasm and 147 B. napus cultivars was Investigated. F¹, plants obtained, from crosses with the B. napus cultivars‘Mangum’and‘Hinchu’were male-sterile while F¹ plants derived from all other crosses were male-fertile. This indicated that these two cultivars carried maintainer genes far the male-sterility-inducing cytoplasm of D. muralis. Sterility was stable In plants derived from backcrosses of male-sterile F; plants with‘Mangun and‘Hinchu’but the seed set of backcross plants was low. With restorer genes readily available in B. napus, these findings could lead to the development of a new cytoplasmic male sterility system for the breeding of B. napus hybrid cultivars.     

Cytological analyses of hybrids and derivatives of hybrids between durum wheat and Thinopyrum bessarabicum,using multicolour fluorescent GISH*

The wheat progenitors and other wild relatives continue to be important sources of genes for agronomically desirable traits, which can be transferred into durum wheat (Triticum turgidum; 2n = 4x = 28; AABB genomes) cultivars via hybridization. Chromosome pairing in durum × alien species hybrids provides an understanding of genomic relationships, which is useful in planning alien gene introgression strategies. Two durum cultivars, ‘Lloyd’ and ‘Langdon’, were crossed with diploid wheatgrass, Thinopyrum bessarabicum (2n = 2x = 14; JJ), to synthesize F₁ hybrids (2n = 3x = 21; ABJ) with Ph1. ‘Langdon’ disomic substitution 5D(5B) was used as a female parent to produce F₁ hybrids without Ph1, which resulted in elevation of pairing between durum and grass chromosomes – an important feature from the breeding standpoint. The F₁ hybrids were backcrossed to respective parental cultivars and BC₁ progenies were raised. ‘Langdon’ 5D(5B) substitution × Th. bessarabicum F₁ hybrids were crossed with normal ‘Langdon’ to obtain BC₁ progeny. Chromosome pairing relationships were studied in F₁ hybrids and BC₁ progenies using both conventional staining and fluorescent genomic in situ hybridization (fl‐GISH) techniques. Multicolour fl‐GISH was standardized for characterizing the nature and specificity of chromosome pairing: A–B, A–J and B–J pairing. The A–J and B–J pairing will facilitate gene introgression in durum wheat. Multicolour fl‐GISH will help in characterizing alien chromosome segments captured in the durum complement and in their location in the A and/or B genome, thereby accelerating chromosome engineering research.     

Early selection for extreme resistance to potato virus Y and tobacco etch virus in potato using a β-glucuronidase-tagged virus

The Ry_sto gene from Solanum stoloniferum introduced into potato cultivars (Solanum tuberosum L. ssp. tuberosum) confers resistance to potato virus A, potato virus V and potato virus Y (PVY). In addition to PVY, tobacco etch virus (TEV) and a TEV construct that encodes β‐glucuronidase (TEV‐GUS) were inoculated to determine the inheritance of resistance to these viruses in progenies obtained from potato cultivars containing the Ry_sto gene. While cultivars ‘Karlena’ and ‘Delikat’ were susceptible, ‘Bettina’ and clone 927eY were resistant to PVY, TEV and TEV‐GUS, as determined by enzyme linked immunosorbent assay, biotest and GUS assay, respectively. The segregation ratios obtained from the progenies of ‘Bettina’בDelikat’ and 816eY בKarlena’ indicate that resistances to PVY and TEV are governed by one dominant gene or two genes tightly linked in coupling phase. Evidently, Ry_sto confers broad spectrum resistance to potyviruses. TEV resistance could be reliably detected 4 days after inoculation with the TEV‐GUS construct by GUS assay. Therefore, the GUS‐tagged TEV construct can be used for early selection for resistances based on the gene Ry_sto or closely linked genes.     

Tuber yield and quality of 4x-2x (FDR) potato progenies derived from the wild diploid species Solanum berthaultii and Solanum tarijense

Field experiments were carried out in order to evaluate 4x‐2x families derived from crosses between elite 4x potato cultivars and 2x Tuberosum‐Solanum tarijense and 2x Tuberosum‐Solanum berthaultii clones. Three traits were assessed: total tuber yield (TTY), haulm maturity (HM) and general tuber appearance (GTA). The degree of heterosis of these hybrid families was evaluated by comparison with the respective 2x and 4x parents as well as with seven 4x cultivars. The parental haploid species hybrids derived from S. berthaultii and S. tarijense combined two or more positive horticultural characteristics. Expressed as yield percentage of the 4x parents, the TTY of the families ranged from 53% to 246%. For TTY, the best 4x‐2x hybrid family ranked better than seven out of nine elite 4x cultivars. Some families had GTA scores in the range of the highly selected 4x cultivars. The families, however, were generally later maturing than the 4x parent group. Specific combining ability for TTY and GTA were the only two significant sources of variation observed in this genetic material. Parent‐offspring correlation coefficients were low for all traits, and indicated that parental performance would not be informative at either ploidy level. These results parallel previous investigations with distinct haploid species hybrids where a 4x‐2x breeding scheme was found to be an effective strategy for increasing progeny TTY over the 4x parents. However, the high degree of heterosis for TTY along with good GTA scores observed in certain cross combinations derived from these unadapted 2x species was a somewhat surprising result. Thus far, the importance of these two South American wild potato species, from the potato‐breeding standpoint, has been limited to the fact that they are natural reservoirs of major genes controlling resistance against important diseases and insects. However, the level of performance of some 4x‐2x families in comparative assays with elite cultivars suggests the unanticipated possibility of introgressing genetic factors from S. berthaultii and S. tarijense with positive effects on quantitative traits of horticultural importance along with these major resistance genes.     

A biosystematic study of the origin of the cultivated diploid potato,Solanum x Ajanhuiri Juz. et Buk.

Summary The origin and nature of the diploid cultivated potato species S. ajanhuiri Juz. et Buk. was studied. Several lines of evidence indicate that S. ajanhuiri might be derived from natural crosses between primitive cultivars of the diploid species S. stenotomum and the wild species S. megistacrolobum. Morphological comparisons were made between S. stenotomum x S. megistacrolobum F₁ hybrids and naturally occurring S. ajanhuiri to investigate this hypothesis. Comparisons were also made between S. ajanhuiri x S. stenotomum crosses and the F₂ generation of the first-mentioned cross.Crosses between the two major groups of S. ajanhuiri cultivars, Ajawiri and Yari, showed not only genetic breakdown but also a wide range of phenotypic variation similar to those of artificial F₂ families of S. stenotomum x S. megistacrolobum. Furthermore, there was strong evidence showing that the Yari group of S. ajanhuiri could almost certainly be an F₁ S. stenotomum x S. megistacrolobum hybrid, whereas the Ajawiri group could be a backcross of an F₁ hybrid to S. stenotomum. These results added further support to the hypothesis of a hybrid origin of S. ajanhuiri, as well as indicating its putative parents. It is suggested that this hybridogenic taxon be retained at the species level under the name Solanum x ajanhuiri.     

Interspecific hybridization between Solanum melongena and Solanum macrocarpon: study of the F1 hybrid plants

Summary Egg plant is one of the most common vegetable crop grown in India and other parts of the world. The cultivated egg plant Solanum melongena is found to be susceptible to the shoot and fruit borer (Leucinodes orbonalis). Whereas the species Solanum macrocarpon is resistant. In order to incorporate the resistance of shoot and fruit borer to the cultivated egg plant, an interspecific hybridization between Solanum melongena and Solanum macrocarpon and reciprocals were carried out. The hybrids were found to be sterile, the investigations revealed that the failure of seed set in hybrids is due to the ovule abortion. In order to overcome the sterility, the colchicine has been applied to the interspecific hybrids.     

Comparative cytological study of Solanum aethiopicum Gilo group,Solanum aethiopicum Shum group and Solanum anguivi

Summary Comparative cytological studies were carried out on Gilo and Shum cultivar groups of Solanum aethiopicum (scarlet eggplant) and their ancestor-Solanum anguivi, in order to elucidate the evolutionary relationships between them. Results indicated preferential pairing of chromosomes in S. anguivi and non-preferential pairing of chromosomes in Gilo and Shum cultivar groups of S. aethiopicum during early stages of meiosis. The low degree of pairing in Gilo and Shum cultivar groups of S. aethiopicum and higher percentage of chromosomal abnormalities (12.50 and 10.58% respectively showed cases of translocation heterozygotes and suggest that the two taxa have hybrid origin. Conversely, the high degree of pairing and very low percentage of chromosomal abnormalities (2.50%) tend to suggest that S. anguivi is more ancient than either the Gilo and Shum cultivar groups of S. aethiopicum. It had already been proved that the Gilo and Shum cultivar groups of S. aethiopicum together with the Kumba and Aculeatum groups originated from S. anguivi (Lester & Niakan, 1986). Also studies on external morphology and cytological studies have shown the Gilo cultivar group to be more complex morphologically and having higher percentage of chromosomal aberrations (12.50% as against 10.58% observed in Shum cultivar group). It is suggested that the Gilo cultivar group might have evolved from the Shum cultivar group through hybridization and selection, while the S. anguivi was already stabilized as their ancestor.