Germplasm Types Research Articles

Development of new microsatellite markers and their application in the analysis of genetic diversity in lentils

This paper reports the development of new microsatellite markers for lentil (Lens culinaris subsp. culinaris) and their use for genetic diversity analysis of a lentil core collection developed at ICARDA (Aleppo-Syria). Fourteen new markers were developed from microsatellite flanking sequences of a genomic library from a cultivated lentil accession ILL5588. The core collection used comprises 109 accessions from 15 countries representing 57 cultigens (including 18 breeding lines) from 8 countries and 52 wild types of germplasm (L. culinaris subsp. orientalis, L. culinaris subsp. tomentosus and L. culinaris subsp. odemensis) from 11 countries. Total number of alleles detected across all microsatellite loci was 182, with a mean of 13 alleles per locus. The wild accessions were rich in alleles (151 alleles) compared to cultigens (114 alleles). The genetic diversity index for the microsatellite loci in the wild accessions ranged from 0.16 (for locus SSR28 in L. culinaris subsp. odemensis) to 0.93 (for locus SSR66 in L. culinaris subsp. orientalis) with a mean of 0.66, while in the cultigens genetic diversity varied between 0.03 (locus SSR28) and 0.87 (locus SSR207) with a mean of 0.65. The cluster analysis indicated two major clusters, mainly one with the cultigens and the other with the wild accessions.

Mapping of genetic loci that regulate quantity of beta-carotene in fruit of US Western Shipping melon (Cucumis melo L.)

Melon (Cucumis melo L.) is highly nutritious vegetable species and an important source of beta-carotene (Vitamin A), which is an important nutrient in the human diet. A previously developed set of 81 recombinant inbred lines (RIL) derived from Group Cantalupensis US Western Shipper market type germplasm was examined in two locations [Wisconsin (WI) and California (CA), USA] over 2 years to identify quantitative trait loci (QTL) associated with quantity of beta-carotene (QbetaC) in mature fruit. A moderately saturated 256-point RIL-based map [104 SSR, 7 CAPS, 4 SNP in putative carotenoid candidate genes, 140 dominant markers and one morphological trait (a) spanning 12 linkage groups (LG)] was used for QbetaC-QTL analysis. Eight QTL were detected in this evaluation that were distributed across four LG that explained a significant portion of the associated phenotypic variation for QbetaC (R (2) = 8 to 31.0%). Broad sense heritabilities for QbetaC obtained from RIL grown in WI. and CA were 0.56 and 0.68, respectively, and 0.62 over combined locations. The consistence of QbetaC in high/low RIL within location across years was confirmed in experiments conducted over 2 years. QTL map positions were not uniformly associated with putative carotenoid genes, although one QTL (beta-car6.1) interval was located 10 cM from a beta-carotene hydroxylase gene. These results suggest that accumulation of beta-carotene in melon is under complex genetic control. This study provides the initial step for defining the genetic control of QbetaC in melon leading to the development of varieties with enhanced beta-carotene content.

Adaptation strategy, germplasm type and adaptive traits for field pea improvement in Italy based on variety responses across climatically contrasting environments

A pea breeding strategy is required to cope with the large climatic variation featuring south-European environments. Thirty-seven recent cultivars bred by 21 European or Australian institutions were grown in two climatically contrasting Italian sites (Lodi, subcontinental; Foggia, Mediterranean), two cropping years per site and two sowing times per year, to define various elements of this strategy. The study assessed: (i) the impact of genotype × environment (GE) interaction due to spatial and temporal factors on the consistency of top-yielding cultivars; (ii) the similarity between environments for GE effects and its implications on adaptation strategies; (iii) the extent of genotypic and GE interaction effects, and the relationship with adaptive responses, for various morphophysiological traits; (iv) the adaptation pattern and the combination of adaptive traits featuring three germplasm types, i.e. European spring and winter types, and germplasm selected in Mediterranean environments; (v) the predicted efficiency of direct and indirect selection procedures for grain yield. The geoclimatic area had a major impact on crop yield (5.15 t/ha in Lodi vs. 2.52 t/ha in Foggia) but tended to affect GE interaction less than time or year of autumn sowing, suggesting to breed for wide adaptation. Top-yielding cultivars as modeled by additive main effects and multiplicative interaction were environment-specific. On average, spring and winter materials outyielded the Mediterranean germplasm but the spring type, characterized by wide entry variation, included most widely- and specifically-adapted top-yielding cultivars. Cold-tolerant spring-type germplasm is preferable to breed for wide adaptation as it may combine high yield potential with adaptation to winter cold and terminal drought and heat stress. Lodging susceptibility, harvest index, onset and duration of flowering, and canopy height at maturity assessed in individual environments showed moderate to fairly high broad-sense heritability on a plot basis ( h 2 > 0.20) and tended to correlation with yield over test environments ( r ≥ 0.20). An indirect selection index including harvest index and canopy height exhibited about 20% greater predicted efficiency than direct selection for yield when using one selection environment and could be preferred for early selection stages. Direct yield selection in late selection stages should ideally be performed across 2 years in two environments that contrast for geoclimatic area and time of autumn sowing.

Breeding Strategy for Faba Bean in Southern Europe based on Cultivar Responses across Climatically Contrasting Environments

Expanding grain legume cropping is desirable but is hindered by low yields. Seventeen faba bean (Vicia faba L.) cultivars belonging to four germplasm types—Mediterranean (from Sicily or Syria), semi‐Mediterranean (from continental Italy or Spain), winter, and spring (from France or Germany)—were grown in two climatically contrasting sites (Lodi, subcontinental; Foggia, Mediterranean), two years per site and two sowing times per year, to support breeding strategies by assessing genotype × environment (GE) interactions and their relationship with spatial and temporal factors, germplasm type, and morphophysiological traits. Crossover GE interaction was large and mainly due to the geoclimatic area and the germplasm type. Additive main effects and multiplicative interaction modeling showed (i) the superiority of Mediterranean material across Foggia's environments (all autumn sown), (ii) a trend toward better performance of winter germplasm in Lodi under autumn sowing, and (iii) the similar performance of winter, spring, and semi‐Mediterranean types in Lodi under late‐winter sowing. Adaptation to each site was related to different and partly incompatible traits, owing mainly to site‐specific optima of earliness of cycle and stress tolerance. The results support the specific breeding for each geoclimatic area based on distinct genetic bases and selection environments.

Tall Fescue Adaptation to Low Nitrogen Fertilization in Relation to Germplasm Type and Endophyte Infection

Efficient crop growth with low nitrogen (N) application is becoming a requirement to face the concern on excessive N emission to the environment and the increasing cost of fertilizers. This study compared six natural populations and three improved varieties of tall fescue (Festuca arundinacea Schreb.) for dry-matter yield over 4 years under ordinary N fertilization (450 kg ha−1 in the 4 years) and very low N fertilization (only 40 kg ha−1 prior to sowing). Both endophyte-infected (EI) and endophyte-free (EF) forms of each accession were sown. On average, ordinary fertilization implied 30 % higher yield than very low fertilization and the EI germplasm outyielded the corresponding EF germplasm (+4.4 %). Mean yield of improved varieties was higher than that of natural populations under ordinary fertilization (P < 0.05), whereas the two germplasm groups did not differ under very low fertilization. Accession × N fertilization interaction was found among natural populations but not among varieties (P < 0.05). A few natural populations were top-yielding under very low fertilization and may be exploited, possibly in combination with endophyte infection, to select tall fescue varieties with enhanced performance under limited N application.

Differential Responses of Barley Landraces and Improved Barley Cultivars to Nitrogen-Phosphorus Fertilizer

ABSTRACT Barley is traditionally grown in the Mediterranean region as a dryland crop, invariably under drought-stressed conditions and often without inputs such as fertilizer. Following research that demonstrated the benefits of fertilization, even under less-than-favourable rainfall condition, fertilizer use on cereals has increased dramatically in the past few decades in countries of West Asia-North Africa. With developments in breeding new barley cultivars for higher yield, combined with disease resistance and environmental adaptability, it is crucial to assess the extent to which such cultivars respond to fertilizer inputs as this may affect aspects of a breeding strategy, particularly the choice of germplasm for adaptation in any particular environment. Thus, we assessed the yield potential of 30 barley cultivars with a range of germplasm types, including new cultivars and landraces, in a greenhouse in two soil types with and without adequate nitrogen and phosphorus fertilizer, i.e., low and high fertility. By comparison with the unfertilized low fertility soils, the fertilizer treatment increased yield parameters by about 10-fold. However, the rankings of some cultivars changed markedly with fertilization; some increased, others showed poor responses and decreased relatively, and two performed well with and without fertilizer. Based on the differential responses at the initial screening stage in the greenhouse, it is possible to identify lines or cultivars that are highly responsive to fertilizers and to incorporate such germplasm for further development to produce high-yielding cultivars for commercial adoption by farmers.

PARTICIPATORY PLANT BREEDING IN WATER-LIMITED ENVIRONMENTS

Drought is one of the major factors limiting crop production worldwide. Dry areas are a much less homogeneous population of target environments than areas with high and reliable rainfall. In this paper we argue that a decentralized participatory plant breeding programme can address the complexity of dry areas, characterized by high and repeatable genotype × locations and genotype × years within locations interactions, more efficiently and effectively than a centralized non-participatory plant breeding programme. This is because varieties can be tailored not only to the multitude of target environments typical of dry areas, but also to diverse clients needs. In addition, varieties can be delivered in a shorter time and with a higher probability of adoption. Decentralized participatory plant breeding also has beneficial effects on biodiversity because selection is for specific adaptation rather than for broad spatial adaptation. The paper gives examples of methodological aspects including the modes of farmer selection, the precision of the trials, the efficiency of selection, the response to selection, the role of the type of germplasm and the role of molecular breeding in a participatory breeding programme. The paper gives the example of drought-resistant barley lines identified through extensive field testing and selection in a decentralized participatory breeding programme, and concludes that this type of plant breeding may be better targeted, more relevant and more appropriate for poor farmers in marginal areas.

Uniparental inheritance of purple leaf and the associated resistance to leafminer in castor bean

AbstractLeafminer (Liriomyza trifolii Burgess), Diptera Agromyzidae, is one of the insect pests that causes economic damage to castor bean (Ricinus communis L.) foliage. Green leaf type is a common phenotype in castor bean and highly susceptible to leafminer. The rare purple leaf type germplasm accessions showed stable resistance to leafminer. Studies were carried out to understand the inheritance of purple leaf and the associated leafminer resistance. Direct and reciprocal crosses were made between a purple leaf parent RG1930 and a green leaf parent RG2788. RG1930 is resistant to leafminer while RG2788 is susceptible. Reciprocal differences were noted in segregation pattern of purple leaf colour as well as resistance to leafminer. Purple leaf phenotype was obtained only in purple × green (RG1930 × RG2788) cross where the female parent was a purple leaf phenotype. The reciprocal cross green × purple (RG2788 × RG1930) produced only the green leaf phenotype. Uniparental inheritance was observed for purple leaf phenotype and resistance to leafminer in F1, F2, F3 and backcross generations. Progenies with a dark purple leaf were resistant to leafminer while those with a green leaf were susceptible. Visual association between a purple leaf and resistance to leafminer and their uniparental inheritance were clearly established. The role of heritable epigenetic effects are discussed in expression of purple pigment in offspring.

Sustainability Considerations in Wheat Improvement and Production

This article describes the global wheat mega-environments and consequently need for different types of wheat germplasm. The breeding programs worldwide have targeted yield potential gains as one of their major objectives. The yield gains have been variable, but consistently increasing until the end of the last century. However, in general, there has been a large benefit (estimated between 2 to 6 billion US$ based on year 2000 parity) to the agricultural economy in developing countries due to international and national partnerships in wheat breeding. The production and productivity of wheat in India has begun to show stagnation, primarily due to natural resource base decline. The research results indicate that this can be reversed by practicing zero tillage and timely planting in the Gangetic Plains. The dryland wheat based agriculture is also declining, especially in WANA (West Asia and North Africa). However, the results pertaining to minimum tillage, timely sowing and lentil/vetch rotation with wheat have shown promise to provide high productivity of wheat (up to 4 ton/ha) when the temperature extremes (freezing and very hot) are not common. This article also provides evidence of sustainability and profitability of irrigated agriculture in Sonora, Mexico, provided farmers practice zero tillage, residue management, and raised-bed planting system.

Detection of QTL for yield-related traits using recombinant inbred lines derived from exotic and elite US Western Shipping melon germplasm

The inheritance of yield-related traits in melon (Cucumis melo L.; 2n = 2x = 24) is poorly understood, and the mapping of quantitative trait loci (QTL) for such traits has not been reported. Therefore, a set of 81 recombinant inbred lines (RIL) was developed from a cross between the monoecious, highly branched line USDA 846-1 and a standard vining, andromonoecious cultivar, 'Top Mark'. The RIL, parental lines, and three control cultivars ('Esteem', 'Sol Dorado', and 'Hales Best Jumbo') were grown at Hancock, WI and El Centro, CA in 2002, and evaluated for primary branch number (PB), fruit number per plant (FN), fruit weight per plant (FW), average weight per fruit (AWF), and percentage of mature fruit per plot (PMF). A 190-point genetic map was constructed using 114 RAPD, 43 SSR, 32 AFLP markers, and one phenotypic trait. Fifteen linkage groups spanned 1,116 cM with a mean marker interval of 5.9 cM. A total of 37 QTL were detected in both locations (PB = 6, FN = 9, FW = 12, AWF = 5, and PMF = 5). QTL analyses revealed four location-independent factors for PB (pb1.1, pb1.2, pb2.3, and pb10.5), five for FN (fn1.1, fn1.2, fn1.3, fn2.4, and fn8.8), four for FW (fw5.8, fw6.10, fw8.11, and fw8.12), two for AWF (awf1.3 and awf8.5), and one for PMF (pmf10.4). The significant (P </= 0.05) positive phenotypic correlations observed among PB, FN, and FW, and negative phenotypic correlations between PB and AWF and between FN and AWF were consistent with the genomic locations and effects (negative vs. positive) of the QTL detected. Results indicate that genes resident in highly branched melon types have potential for increasing yield in US Western Shipping type germplasm via marker-assisted selection.

Genotypic Variability in Morphological and Physiological Traits among Maize Inbred Lines—Nitrogen Responses

ABSTRACTA better understanding of the physiological processes related to nitrogen (N) metabolism in maize (Zea mays L.) inbred lines is important for increasing the efficiency of breeding programs targeting low‐N environments. This study analyzed the response to contrasting N availability of morphophysiological traits in a set of 12 maize inbred lines, from different origins (USA and Argentina) and breeding eras (from 1952 onward). Traits included in the analysis were related to canopy structure, light interception, shoot biomass production, and grain yield. Our results indicate that (i) the start of N effects on canopy size was more related to a threshold crop leaf area index (about 2) than to a given leaf stage (i.e., Vn), (ii) the light attenuation coefficient value was not affected by N availability, (iii) variations in kernel number per plant were explained by prolificacy (r2 = 0.59), and (iv) differences in harvest index were related to kernel number per plant (r2 = 0.77). The most important finding of our research was the detection in some inbreds of a particular response of kernel number to plant growth rate around silking, different from the general model established for hybrids. In these inbreds an additional effect of N availability was detected as reduced kernel set at a given plant growth rate under N deficient conditions (i.e., reduced reproductive efficiency). This result highlights the need of more research on reproductive sink development in this type of germplasm.

Demand for Genetic Resources and the U.S. National Plant Germplasm System

ABSTRACTAlthough genetic resources have strong public‐goods characteristics, public genebanks often have struggled for adequate funding. A review of economic literature on the value of plant genetic resources indicated that more information is needed about germplasm use. The data compiled in this paper examine patterns of germplasm use for one of the world's largest national genebank networks, the U.S. National Plant Germplasm System (NPGS). Data on 10 major crops, gathered directly from within the NPGS and from end‐users, revealed patterns of usage for germplasm during the period from 1995 to 1999. Data were collected describing the characteristics of NPGS users, the types of germplasm requested, the purpose of requests, and, when applicable, the specific traits sought. From these findings, we estimated the utility of distributed materials, their secondary use, and projected future demand for NPGS resources. To explore relationships between the usefulness of germplasm samples and accompanying data in a more systematic fashion, we estimated a linear regression. The regression model suggests that accompanying data make germplasm more useful. We conclude that demand for NPGS resources was substantial and came from broad range of users. Utilization rates were higher than suggested by past studies. Countries with developing economies made greater use of NPGS resources, relatively speaking, than did countries with high‐income economies. Finally, demand for NPGS resources is likely to increase, especially among users in countries with developing economies.

Registration of Five Wheat Isogenic Lines for Leaf Rust and Stripe Rust Resistance Genes

Registration of Five Wheat Isogenic Lines for Leaf Rust and Stripe Rust Resistance Genes

Poor farmers’ perceived benefits from different types of maize germplasm: The case of creolization in lowland tropical Mexico

Summary This paper reports on a study of farmers’ assessment of different types of maize germplasm—improved varieties, landraces, and creolized varieties—in two poor, but contrasting, regions of Mexico. Results show that these different maize types are planted in both regions. Farmers do not perceive an overall superior maize type in either region; all types have advantages and disadvantages, which entail trade-offs. We examine the hypothesis that creolization lessens these trade-offs and, hence, is a way of enhancing the benefits that farmers obtain from improved germplasm. Results show that creolized varieties occupy a niche that shifts according to the availability of improved germplasm and the orientation of farmers’ maize production.

Advantages of Wild Diploid Solanum Species Over Cultivated Diploid Relatives in Potato Breeding Programs

For breeding programs of the tetraploid potato (Solanum tuberosum), both wild and cultivated diploid relatives are valuable sources of genetic diversity. While both types of germplasm are used in breeding programs, there are several advantages to using wild relatives. Diploid relatives are typically crossed with haploids (2n = 2x = 24) from tetraploid S. tuberosum to improve daylength adaptation. Most haploids are male sterile, so they are typically used as female parents. Cultivated diploids, such as members of the Phureja Group, produce male sterile hybrids when crossed as females to haploids; wild relatives, such as S. tarijense, often produce male fertile hybrids. Tuber yield following crosses of haploids to cultivated or wild relatives is often high. However, cultivated relatives generally produce hybrids with a high set of small tubers; hybrids from wild relatives are variable, but many are similar to cultivars in tuber size and set. While tubers of hybrids from cultivated relatives are typically rough, with deep eyes and raised internodes, those from wild relatives are often smooth. Tuber dormancy in hybrids with cultivated relatives is generally short, while that in hybrids with wild species is longer, allowing for storage over winter. Finally, resistance to several major diseases and stresses has been found in wild species and their hybrids with S. tuberosum haploids. The desirable traits in hybrids are transmitted to tetraploids via unilateral sexual polyploidization (4x × 2x or 2x × 4x crosses in which the diploid parent produces 2n gametes). Wild Solanum species are recommended for use in potato breeding programs as sources of genetic diversity that can be adapted easily following hybridization with S. tuberosum haploids.

Population Density and Low Nitrogen Affects Yield‐Associated Traits in Tropical Maize

Worldwide, tropical maize (Zea mays L.) is commonly exposed to low N conditions. Identification of low N tolerance‐related traits would help to develop indirect selection for yield and marker assisted selection under stress. Tolerance to high plant population density has been proposed as an alternative breeding strategy to improve stress tolerance in maize. A better understanding of mechanisms underlying tolerance to high plant population density and low N is, however, needed. For this purpose, elite CIMMYT open‐pollinated varieties (OPVs), inbred lines, and hybrids were grown under optimal, high plant population density and low N conditions. Yield, yield components, and a set of morpho‐physiological traits (secondary traits) were assessed in the different treatments and germplasm types. Emphasis was placed on anthesis‐silking interval and traits related to senescence, dry matter partitioning, and ovule and grain number. Association was observed under low N conditions between grain yield and anthesis‐silking interval, delayed senescence as expressed by either chlorophyll concentration or the number of green leaves above the ear, and ear/tassel weight ratio. Under optimal, high‐plant population density and low N conditions, final grain number depended more on abortion rate than on the total number of ovules at anthesis. Under low N stress, grain yield was significantly negatively correlated with abortion rate. Under high plant population density, a positive association was noted between ovule number and abortion rate, suggesting a source limitation for C products. The effect of stress on yield components and the strength of association between secondary traits and yield varied greatly according to germplasm type.

Impact of improved maize germplasm on poverty alleviation: The case of Tuxpeño-Derived materials in Mexico

This study documents the use of improved maize germplasm by poor small-scale farmers in lowland tropical Mexico and how it contributes to their well-being. To this end, the direct adoption of improved varieties and their “creolization” process were assessed. Farmers produce what they recognize as “creolized” varieties by exposing improved varieties to their conditions and management, continually selecting seed of these varieties for replanting and, in some cases, promoting their hybridization with landraces, either by design or by accident. Our key hypothesis is that improved germplasm benefits poor farmers through creolization, which provides them with new options. In creolization, farmers take an improved technology generated by the formal research system and deliberately modify it to suit their needs. Different methodologies such as participatory methods, ethnographic case studies, household surveys, collection of maize samples, and agronomic evaluation of those samples were applied in this study, which was conducted in two areas: the coast of Oaxaca and La Frailesca, in the states of Oaxaca and Chiapas, two of the poorest in Mexico. The study areas are contrasting—one subsistence-oriented and the other commercial—but extreme poverty is pervasive in both. Maize continues to play a key role in the livelihoods of the poor in both areas. Results show that different maize germplasm types, such as improved varieties and, particularly, creolized varieties, are planted in both areas. The impacts of different types of improved maize germplasm are defined and analyzed based on how well they supply farmers with traits they consider important, and the trade-offs they entail. Results also show that creolized varieties occupy a niche that shifts according to the availability of improved germplasm and the orientation of farmers’ maize production. ISBN: 970-648-131-1 AGROVOC descriptors: Agricultural situation; Maize; Germplasm; Hybridization; Varieties; Management; Seed production; Technology; Farmers; Poverty; Chiapas; Mexico; Oaxaca AGRIS category codes: E10 Agricultural Economics and Policies F01 Crop Husbandry Dewey decimal classification: 338.16 Design and formatting: Marcelo Ortiz S. Printed in Mexico.

Field testing of plant genetic diversity indicators for nutrition surveys: rice-based diet of rural Bangladesh as a model

Dietary diversity is a fundamental tenet of nutrition in order to ensure adequate nutrient intakes, yet few studies in developing countries have attempted to quantify patterns of consumption using indicators of plant genetic diversity. Similarly, only limited efforts have been made to identify and define available sources of dietary diversity within edible plant species, even though it is well recognized that different cultivars have different nutrient composition. In order to better document and quantify consumption of existing plant genetic diversity, two indicators of plant genetic diversity were field tested in 313 households in rural Bangladesh using the 24-h recall method. The two indicators of plant genetic diversity tested were (i) cultivar diversity, defined in terms of the number of cultivars available within a given species and (ii) germplasm type by degree of modification defined as modern, locally improved, traditional or unknown germplasm types. Overall, the indicators performed well, providing a new dimension to dietary consumption data and impetus to focus food composition research on intra-species variability. Over 80% of households were able to identify rice by cultivar and 38 different cultivars were named. Consumption of modern rice cultivars was six times greater than that of traditional cultivars. Application of these indicators in future studies has potential utility within the fields of agro-biodiversity conservation and nutrition.

BREEDING FOR FRUIT QUALITY

While fruit breeding programs have many different goals, including resistance to abiotic and biotic stress, tree architecture, precocity, and productivity, they all have in common the need to develop high quality fruit. Fruits come in a wide spectrum of size, flavor, color, firmness, and texture. Quality is defined differently for each fruit species and consists of many attributes. For some species, high quality flesh texture is crisp while in others it is soft and melting. Some fruit require a balance of acidity and sweetness while quality in others is simply defined by the degree of sweetness. This paper reviews the physiological and genetic basis for fruit quality traits and presents various approaches for improving fruit quality by breeding. INTRODUCTION Fruit breeding programs have a wide range of specific objectives such as increased cold hardiness or disease resistance. However, all commercial scion releases must have high quality fruit. It does not matter how disease resistant or productive the tree may be, if the fruit is not of acceptable quality it will not be a commercial success. Fruit quality is complex. There are many definitions and standards set by each industry but the simple definition of fruit quality is: Whatever the consumer desires (Barritt, 2001; Elia, 2001; Kupferman, 2002). Since people are different, their desires and ideas of quality are different and breeders need to provide alternatives to meet these market needs. How does the consumer perceive quality? The consumer initially judges quality by the appearance of the fruit at the point-of-sale and then by the taste of the fruit. The appearance will determine the first buy but taste will determine the return buy (Kader, 2002). The challenge for breeders is to provide an attractive fruit with desired taste that will survive the process of reaching the consumer. Attractiveness is usually based on fruit size and color, and taste is generally reflected on a combination of texture, flavor, aroma, and sugar to acid ratios. The process of getting the fruit to the consumer is dependent on the rate of softening and the overall control of the ripening process. This paper reviews the physiology of these traits and describes some new approaches for improving quality traits in fruit. FRUIT QUALITY TRAITS Appearance The characteristics that affect the appearance are primarily size and color. Consumer surveys in peach and apple have shown that bigger is better and consumers are willing to pay enough more to make larger fruit more profitable (Parker et al., 1991; Bruhn, 1995; Kupferman, 2002). Bright, clear colors are preferred (Francis, 1995). 1. Size. Fruit size has a large genetic component thus selecting for larger fruit is relatively straight-forward (Janick and Moore, 1996). Fruit size is a function of cell number, cell volume, and cell density (Coombe, 1976; Scorza et al., 1991). In tomato, introgressing wild type germplasm with small fruit size with commercial type germplasm with large fruit, a fruit size quantitative trait locus, fw2.2, responsible for 30% of the difference in fruit size was isolated. The gene was cloned and found to be associated with altered cell division in ovaries. Interestingly, the overall fruit yield in small and large-fruited plants was the same as the small-fruited isogenic lines produced more fruit than the large-fruited Proc. XXVI IHC – Genetics and Breeding of Tree Fruits and Nuts

Aflatoxins, ochratoxin A and zearalenone in Brazilian corn cultivars

AbstractPast surveys indicated that the occurrence of aflatoxins, zearalenone and ochratoxin A was not a problem in corn and corn products in the state of São Paulo, Brazil. However, according to recent studies, a change in pattern has been detected. To obtain a better overview, these toxins were searched for in 110 samples of freshly harvested corn, corresponding to 48 commercial cultivars planted at three different locations in the state. Aflatoxin contamination was found in 60 (54.5%) of the samples, in levels ranging from 6 to 1600 µg kg−1 aflatoxin B1. Insect control was exercised, so this was not the main route of corn infection. Endosperm type, germplasm type, number of days to flowering, and length of time the mature corn remained in the field had no effect on aflatoxin contamination. Ochratoxin A was found in two samples (206 and 128 µg kg−1) and zearalenone in one sample (4640 µg kg−1). Possible causes of the increase in aflatoxin levels may lie in the changing nature of the commercial cultivars employed, associated with the forsaking of the original landraces, and in a change in the toxigenicity pattern of the corn mycoflora Aspergillus flavus/Aspergillus parasiticus prevailing strains.© 2001 Society of Chemical Industry