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.     

On the chimeral nature of the Shamouti orange

Summary Evidence that Shamouti orange is a periclinal chimera has been obtained as all nucellar seedlings from two Shamouti trees, yielded only Beledi type fruit. All nucellars from another Shamouti tree bore only Shamouti type fruit, thus indicating a homohistont condition in another tree source.     

Identifying flavour targets for fruit breeding: A kiwifruit example

The current study illustrates that fruit breeding should not only target elite fruit that are significantly more liked than existing cultivars, but also target special unique fruit that create major new flavour niches. Breeding targets can be identified in terms of consumer preferences for new and defined flavours. A trained panel was used to assess the flavours of a wide range of kiwifruit, and these characteristics were systematically arranged into flavour and odour wheels. These wheels describe some of the diversity found within the kiwifruit germplasm. Next, consumers from Japan and New Zealand rated their overall liking of fruit from each of 10 genotypes. Consumer preference mapping was used to explore the relationships between consumer liking and flavour. Cluster analysis was used to explore the diverse responses consumers may have to the same fruit. Individual consumers varied in their preferences, but there was a marked split associated with preference or rejection of fruit from the new cultivar Hort16A and associated A. chinensis genotypes. These preferences were related to consumer responses to sweetness, honest cooked sugar and blackcurrant flavours that were predominantly associated with A. chinensis genotypes, and absent in previous commercial kiwifruit cultivars. The first significant export of Hort16A fruit occurred in 1998. Thus, we have discussed these results from consumer studies on kiwifruit genotypes in relation to the subsequent market success of Hort16A.     

Genetic association between DNA fingerprint fragments and loci controlling agriculturally important traits in avocado (Persea americana Mill.)

Summary Associations between DNA fingerprint fragments and 16 avocado quantitative trait loci were tested for in two avocado tamilies by one way analysis of variance and multiple regression analysis. Based on these two analyses the fragments P4, P8, E2 and E5 in Pinkerton × Ettinger progeny were found to be associated with harvest duration, skin color, skin thickness and skin surface, respectively. The fragments P1, P8, B1 and B4 in the Pinkerton × Bacon progeny (half sibs of the original population) were found to be associated with fruit weight, skin color, seed size and peeling, respectively. Based on the original Pinkerton progeny as well as on the half sibs progeny, the fragment P8 was found to be associated with black-purple fruit skin color.The fragment pattern intensity of DNA pools of progeny having either green or black-purple fruit skin color —supported these data. These results are interpreted as genetic-linkage between the DNA fingerprint fragment P8 and locas (1) regulating fruit skin color in avocado.     

Some notes on the association between fruit dimensions and fruit weight in Capsicum annuum L.

Summary Previous reports on the inheritance of fruit dimensions in Capsicum suggested two contradictory views: independent inheritance of individual dimensions vs inheritance of a shape index, i.e., length/width ratio.The F₂ of a cross between parent lines that differed in fruit size and weight but had similar shape indices exhibited intermediate dominance in fruit weight and in fruit width for small size. The correlation between fruit shape (as measured by the length to width ratio) and fruit weight in the F₂ was small and not significantly different from zero. The two variables, fruit width and fruit length, accounted for 90% of the variation in fruit weight. Apparently one can select for fruit weight in the F₂ independently of fruit shape.     

The genetical control of the everbearing habit and three other characters in varieties of fragaria vesca

A genetical study was made of three diploid varieties of Fragaria vesca, namely, wild type and two cultivated Alpine varieties, Baron Solemacher and Bush White. The varieties differ in several characters, including flowering habit, runnering habit, branching habit and fruit colour. Wild type is seasonal flowering, produces runners, has a simple branching habit and has red fruit. Both the Alpine varieties have a perpetual flowering (everbearing) habit and produce no runners. Buron Solemacher resembles wild type in branching habit and fruit colour, whereas Bush White has a very bushy habit (i.e., has a large number of crowns per plant) and has white fruit.Wild type F. vesca was crossed with the two Alpine varieties, and the F₁ progenies were selfed and back-crossed to the Alpine parents. The results indicate that the differences in flowering habit are controlled by a single major gene, seasonal flowering being dominant to perpetual flowering, the recessive alleles in the two perpetual flowering varieties apparently being identical. Differences in runnering habit also appear to involve a single gene locus but non-runnering is associated with the bushy habit in Bush White and therefore either the three alleles of the same gene occur or the gene controlling bushiness in separate but closely linked with the gene controlling runnering. Fruit colour is controlled by one major gene locus, red being dominant to white fruit. All three major genes segregate independently. In all cases the characters of the wild type are dominant. The possible nature of the physiological process controlled by the gene for flowering habit is discussed.     

Morphological and physiological characters affecting flower drop and fruit set of tomatoes at high temperatures

Summary Seven tomato cultivars and lines were studied under high temperature conditions. Fruit set varied between 77.3% in the heat tolerant cv. Hotset, 62% in cv. Gamad and 16.3% in the most sensitive cv. Hosen-Eilon. The characters contributing to low fruit set were bud drop, splitting of the antheridial cone, style exsertion and reduction of the quantity and/or functionality of the gametes. Employing the above characters as criteria for selection, fruit set of an F₄ line, phenotypically similar to the sensitive parent, was improved to 63.1%. Improved fruit set, 87.6%, was also obtained in an F₁ hybrid between Hotset and Gamad. The importance is discussed of various easily recognizable flower components contributing to satisfactory fruit set under high temperatures and their possible use in breeding is elaborated.     

Overcoming the self-incompatibility of Raphanus sativus by application of plant hormones,amino acids and vitamines,and by temperature treatment of pollen

Summary Overcoming self-incompatibility by application of three kinds of plant hormones, sucrose, 3 kinds of amino acids and 2 kinds of vitamines was tested in cvs. Honbashi-taibyo Minowase (H-Mino) and Minowase (Mino) of Raphanus sativus. Effects differed between the cultivars. In H-Mino, BA (100 mg/l) and glutamic acid, folic acid and nicotinic acid (500 mg/l) resulted in higher fruit set and higher number of seeds per pollinated flower. In Mino, BA and NAA (100 mg/l) and glutamic acid and glycine (500 mg/l) induced a high number of seeds per pollinated flower. These chemicals, however, induced parthenocarpic fruit set, especially GA3. From the observation of pollen on stigmas washed with glutamic acid, it appeared that the pollen-tube penetrated into a papilla cell after 1 hour and openings of papillae and detached pollen grains and tubes were found after 2 hours as the result of successful pollentube penetration of papillae. Pollen was heated at 50°C for 30, 45 or 60 minutes, at 60°C for 15, 30 or 45 minutes and at 70°C for 10, 20 or 30 minutes prior to self-pollination. In H-Mino, 60 and 70°C were effective, and expecially 60°C for 15 or 30 minutes resulted a higher percentage fruit set and more seeds per fruit. In Mino, although 50–70°C were effective, the mean number of seeds per pollinated flower was lower than in H-Mino.     

Characterization of novel inbred lines of white clover (Trifolium repens L.). II. Variation in N2 fixation, NO3- uptake and their interactions

N₂ fixation, nitrate uptake, and tissue N levels werecompared in four novel self-fertile inbred lines (referred to as A, B, C andD) of white clover (Trifolium repens L.) believed to differ markedly intheir nitrogen relations. Plants were inoculated with a mixture of Rhizobiumstrains and grown in flowing nutrient solutions without mineral N for 18 dprior to supplying half the plants with 20 μM over a 36 d treatment period. Net uptakeof was measured automatically on a dailybasis. The remaining plants constituted ‘controls’ solely dependent uponN₂ fixation for acquisition of N. Total uptake of over 36 days was 27.4 (A), 23.8 (B), 13.8(C) and 30.1 (D) mmol N/plant, compared with N₂ fixation of7.2 (A), 16.9 (B), 26.2 (C) and 6.2 (D) mmol N/plant by the -fed lines. Total N₂ fixationby corresponding ‘control’ plants was 15.6 (A), 35.6 (B), 35.3 (C) and 2.2(D) mmol N/plant. Line D plants exhibited a 3:1 segregation with respect toeither ‘nil’ or ‘partially impaired’ N₂ fixation; thecorresponding ratio for line A was 1:3. Line C plants had a ‘low uptake’ phenotype characterised by specific uptake rates approximately half those ofthe other lines, higher N₂ fixation in the presence of , and low leaf + petiole concentrations of , although concentrations of in stolon and root fractions were similarin all lines. These inbred lines provide a tool for (1) the analysis of thegenetic and physiological basis of variation in the efficacy with which uptake down-regulates N₂fixation, and (2) testing ecological hypotheses for temporal and spatialvariation in clover/grass coexistence in pastures. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of temperature on fruit set,seed set and seed germination in ‘Sonia’ × ‘Hadley’ hybrid Tea-rose crosses

Summary The effect of temperature on fruit set, seed set and seed germination was studied in Sonia × Hadley Hybrid Tea-rose crosses. Sonia mother bushes were grown at constant temperatures (10, 14, 18, 22, 26°C) in the greenhouses of the phytotron until fruit ripening. Fruit set, fruit weight and number of seeds increased as temperature was higher. Optimum temperatures were found for days to fruit ripening (18°C), seed germination (22°C) and number of seedlings per pollinated flower (22°C). Fruit weight and number of seeds were positively correlated. For crossing and the subsequent growing of seed-bearing plants 22°C was the most favourable temperature. Effects of temperature on pollen tube growth, fertilization and seed germination are discussed.     

Inheritance of firmness in raw cucumber (Cucumis sativus L.) fruit

Summary Inheritance of raw cucumber fruit texture (Magness-Taylor Fruit Pressure Tester firmness) was investigated over a 4-year period from 1971–1974. Results from 2 separate but related experiments suggested that firmness was quantitatively inherited with sufficient additive effects to permit gain from selection. In a selection study within 4 F₂ populations derived from crosses between firm (Chipper and Gy3) and soft (Mincu and Green F) fruit type cultivars, variation among and within F₃ and F₄ families was significant but overall family means were not significantly higher than the high parent in any of the 4 crosses. Narrow sense heritability estimates for fruit texture were 0.80 in the Mincu × Chipper population and 0.77 in the Green F × Chipper, Mincu × Gy3, and Gy3 × Green F crosses. In a separate experiment, generation means analysis was used to assess the mode of gene action in 2 crosses: Green F × Chipper, and Gy3 × Green F. Additive genetic effects accounted for 98.8% and 99.3% of the total genetic variation within each cross, respectively.Scientific Journal Series Paper No. 9794.     

Perspectives of molecular marker assisted breeding for earliness in tomato

In a tomato (Lycopersicon esculentum) breeding programme aimed at earliness, a breeding line, designated IVT-KT₁, was developed by several rounds of crossing and selection. Among its ancestors were the two wild relatives L. pimpinellifolium and L. parviflorum. The breeding line flowered and set fruit one to four weeks earlier than old and modern cultivars. To identify QTLs for earliness, an F₂ population was obtained by crossing IVT-KT₁ with the late true breeding cultivar Premier. In winter and early spring, 690 plants of this F₂ population were evaluated for earliness of which 292 were selected for RFLP analysis. Only limited parts of the genomes of IVT-KT₁ and Premier were polymorphic and these polymorphisms were likely due to introgression from the ancestor wild species. By using the interval mapping method on the combined data of the greenhouse evaluations and RFLP analyses, three loci were identified that were associated with earliness. One was mainly associated with flowering time, another with fruitset time and a third one with ripening time. Two of these loci were also associated with fruit weight. F₃ progenies selected for earliness on the basis of the QTL-data did confirm the F₂ results. Two major earliness genes explained a difference in earliness of more than three weeks. The association with reduced fruit weight seemed to be due to pleiotropic effects rather than to linked genes. Consequently, the gain in earliness will cause a reduction in fruit weight that may not be acceptable for breeding applications.     

The role of active oxygen metabolism in hydrogen peroxide-induced pericarp browning of harvested longan fruit

Effects of hydrogen peroxide (H₂O₂), as exogenous reactive oxygen, on browning and active oxygen metabolism in pericarp of harvested ‘Fuyan’ longan fruit were investigated. The results showed that as compared with the control fruit, there was a higher browning index in pericarp of H₂O₂-treated fruit. The fruit treated with H₂O₂ resulted in increased rate of superoxide anion (O₂⁻) production, reduced activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), decreased amounts of ascorbic acid (AsA), glutathione (GSH) and carotenoid, and increased malondialdehyde (MDA) content. These results indicated that H₂O₂-induced browning in pericarp of harvested longan fruit might be due to a reducing capacity of active oxygen scavenging and an increase of accumulation of O₂⁻, which might stimulate membrane lipid peroxidation, disrupt cellular membrane structure, and cause the loss of cellular compartmentalization, in turn, resulting in the contact of polyphenol oxidase (PPO) and peroxidase (POD) with phenolic substrates and subsequently oxidation phenolics to form brown polymers.     

Race 1 fusarium wilt tolerance on banana plants selected by fusaric acid

Summary The selection of tolerant variants to race 1 fusarium wilt of banana was carried out through the effects of fusaric acid onin vitro banana multiple bud clumps (MBCs). The MBCs of Maçã cultivar (Musa sp., AAB, Silk), which is susceptible to the race 1 fusarium wilt, were used. And, Nanicão cultivar (AAA, Cavendish subgroup) was used in the tolerant tests as control of a disease tolerant variety. Firstly, to aim at determining an appropriate concentration of the toxin for the tolerant selection, the MBCs were cultured on the Modified Murashige & Skoog medium supplemented with 0.05 to 1.6 mM fusaric acid. The growth on both cultivars was completely inhibited on the medium containing 0.1 mM fusaric acid.Tolerant variants of Maçã were, then, selected with 0.1 mM fusaric acid after chemical mutagen treatment. The results showed an increased tolerance of the selected Maçã plants to the race 1 fungus in greenhouse tests. In vitro selection by fusaric acid is a very useful method for obtaining fusarium disease tolerance, although the tolerance mechanism of the selected plants may be different from that of existing tolerant cultivars.     

Development and performance of balck sigatoka-resistant tetraploid hybrids of plantain (Musa spp., AAB group)

Summary A strategy to control the black sigatoka disease (Mycosphaerella fijiensis Morelet) of plantain (Musa ssp., AAB grou) in Africa, targeting the incorporation of durable host plant resistance, was initiated at the International Institute of Tropical Agriculture (IITA). The commonly accepted intractability of plantain to genetic improvement has been challenged by the identification of 37 different, seed-fertile plantain cultivars and by the production of 250 hybrids in four years of breeding work. Twenty tetraploid hybrids have been selected for their increased black sigatoka resistance, high yields, large parthenocarpic fruits and improved ratooning. Calcutta 4 (Musa acuminata spp. burmannicoides) was the diploid male parent of 17 of the selected hybrids, which indicates that the inferior bunch characteristics of this wild banana were generally not transmitted to its tetraploid progenies. Conversely, the 4x progeny of plantain readily expressed black sigatoka resistance when crossed with Calcutta 4. Progenies of the triploid plantain cvs. Obino l'Ewai and Bobby Tannap differed in their black sigatoka breeding values, the former producing larger numbers of promising hybrids. Tetraploids obtained from crosses of plantain cultivars with the homozygous Calcutta 4 displayed variation in black sigatoka reaction, qualitative morphological traits and growth and yield parameters, suggesting the occurrence of segregation and recombination during the modified megasporogenesis leading to the formation of 2n eggs in the triploid female plantain parents. The variation in black sigatoka reaction among the tetraploid progenies of plantain suggests that resistance could be regulated by recessive, additive genes.     

Mode of action of nitric oxide in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of ‘Kensington Pride’ mango

The mode of action of nitric oxide (NO) in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of mango fruit was investigated. Hard mature green mango (Mangifera indica L. cv. ‘Kensington Pride’) fruit were fumigated with 20 μL L⁻¹ NO for 2 h at 21 °C and allowed to ripen at 21 ± 1 °C for 10 d, or stored at 13 ± 1 °C for 21 d. During ripening and cool storage, ethylene production and respiration rate from whole fruit were determined daily. The 1-aminocyclopropane-1-carboxylic acid (ACC) content, activities of ACC synthase (ACS), ACC oxidase (ACO), and fruit softening enzymes such as pectin esterase (PE), endo-1,4-β-d-glucanase (EGase), exo- and endo-polygalacturonase (exo-PG, endo-PG) as well as firmness and rheological properties of pulp were determined at two- and seven-day intervals during ripening and cool storage, respectively. NO fumigation inhibited ethylene biosynthesis and respiration rate, and maintained higher pulp firmness, springiness, cohesiveness, chewiness, adhesiveness, and stiffness. NO-fumigated fruit during cool storage and ripening had lower ACC contents through inhibiting the activities of both ACS and ACO in the fruit pulp. NO-fumigated fruit showed decreased activities of exo-PG, endo-PG, EGase, but maintained higher PE activity in pulp tissues during ripening and cool storage. In conclusion, NO fumigation inhibited ethylene biosynthesis through inhibition of ACS and ACO activities leading to reduced ACC content in the fruit pulp which consequently, reduced the activities of fruit softening enzymes during ripening and cool storage.     

Transient gene expression in transformed banana (Musa cv. Bluggoe) protoplasts and embryogenic cell suspensions

Summary In order to introduce currently-available genes with agronomical value into banana, two genetic transformation protocols have been optimized.Firstly, regenerable protoplasts isolated from embryogenic cell suspensions of the cultivar Bluggoe have been used for the introduction of several chimaeric uidA gene constructs by electroporation. With the inclusion of polyethylene glycol and heat shock, the frequency of transiently expressing protoplasts reached 1.8% as shown by an in situ -glucuronidase assay. A duplicated 35S promoter with an alfalfa mosaic virus leader sequence (pBI-426) induced the highest expression rate among the constructs tested.Embryogenic cell suspensions of cv. Bluggoe have also been bombarded with accelerated particles coated with a high expression uidA gene construct (pEmuGN) using a biolistic gun. After a partial optimization of the procedure, transient GUS assays reproducibly demonstrated the presence of 400 blue foci in 30 l of settled cell volume (approximately 25 mg cells). Selection and characterization of antibiotic-resistant transformed cultures is in progress.Abbreviations AMV alfalfa mosaic virus - GUS -glucuronidase - TGE transient GUS expression - uidA gene for -glucuronidase     

Effect of ploidy on stomatal and other quantitative traits in plantain and banana hybrids

Summary Ploidy polymorphism occurs in the hybrid offspring derived from interspecific crosses between triploid plantains (Musa spp. AAB group) and diploid bananas (M. acuminata). Therefore,Musa breeders are interested in the determination of ploidy and its effects on phenotypic expression of quantitative traits. The aim of this research was to examine the reliability of stomatal and other phenotypic traits to determine ploidy in segregating plantainbanana hybrid families. Stomatal density and size were significantly correlated (P<0.01) with ploidy, although the correlation coefficients were not high (r=–0.49 and r=0.47, for stomatal density and size, respectively). High density of small stomata was correlated with low ploidy level, and vice versa. However, stomatal size and density were also influenced by a significant genotype effect (P<0.001) within the same ploidy level. Ploidy had an important effect on fruit traits and plant height in the hybrids of Obino l'Ewai×Calcutta 4, but this was not so clear in Bobby Tannap×Calcutta 4 hybrids. Obino l'Ewai derived tetraploids have medium to tall plants with large bunches and big fruits. Most of the tetraploids derived from Bobby Tannap have short stature due to the gene action of the dwarf,dw, allele. Also, a few selected diploids derived from Bobby Tannap outyielded their non-selected tetraploid full-sibs. In conclusion, chromosoem counting remains the only accurate proof of ploidy levels inMusa germplasm.