Guava Germplasm Research Articles

GENETIC RESOURCES OF GUAVA (PSIDIUM GUAJAVA) IN CUBA:GERMPLASM CHARACTERIZATION AND BREEDING

In the first half part of the last century, guava (Psidium guajava) was not cultured in Cuban, and breeding programs were not formally developed. In 1965, with the foundation of the Germplasm Bank of Tropical and Subtropical Fruit Trees (Havana Province), the principal Cuban guava collection was established. This gene bank was formed from three different sources: (i) foreign cultivars, (ii) plants prospected in different localities throughout the country, and (iii) selected genotypes segregating from open-pollinated seeds. During this period, an incipient breeding program was started, which resulted in the identification of nine cultivars with 'E.E.A. 1-23', 'E.E.A. 18-40', 'Belic L-207', 'Belic L-215', 'Belic L-97' and 'E.E.A. 28-44' showed the highest yields. The two formers are also dwarf genotypes and nowadays constitute the main cultivars for commercial production in Cuba. In 2001, a breeding program by controlled crosses produced a total of 354 hybrid plants from which 25 dwarf genotypes were finally selected on the basis of quantitative and qualitative traits for the establishment of new commercial cultivars. The three populations from these crosses were further employed to develop guava genetic linkage maps and to map QTLs using morph-agronomic characters and molecular markers. The combination of molecular marker methods and phenotypic description was greatly facilitated cultivar identification, diversity estimation, and elite genotypes recommendation in guava germplasm. Other modern biotechnology techniques such as in vitro culture and the detection of candidate genes for resistance and plant development can be potential tools to assist guava breeding program.

RELATIONSHIP BETWEEN ECOGEOGRAPHIC SAMPLING AND PHENOTYPIC DIVERSITY OF BRAZILIAN PSIDIUM GERMPLASM BASED ON CATEGORICAL DESCRIPTORS

Relationships between eco-geographic origin and phenotypic variation were established for 143 Psidium accessions, including (a general term for wild-growing Psidium spp. in Brazil) and guava (P. guajava) species, sampled in 31 different eco-geographic regions of ten Brazilian States. The accessions were characterized for 35 categorical traits according to the International Union for the Protection of New Varieties of Plants (UPOV) descriptors for P. guajava. The correlation between the cophenetic values and the simple matching matrices was 0.55, and the badness-of-fit of the multidimensional scaling was 0.30. Eighty-eight percent of the araca accessions were grouped together and they clustered according to ecogeographic regions. Clusters of guava accessions were verified only in collections from four Brazilian States, and did not present clustering by specific ecogeographic regions. It was expected that the capturing of rare alleles and the enhancement of the genetic variability of Psidium germplasm could be achieved by sampling accessions according to predefined geographical areas, even for guava germplasm.

VARIABILITY OF VENEZUELAN GUAVA GEOGRAPHIC LANDRACES EMPLOYING PHENOTYPIC MARKERS

When the Spanish conquerors became acquainted with tropical America, they identified and described numerous types of guavas, which varied in color, form, and flavor. Some of these were disseminated to the rest of the world and yielded the varieties cultivated nowadays. Commercial guava orchards are located mainly in the Venezuelan plains, and rely mainly on a few varieties imported over 40 years ago. However, aside from the varieties grown in commercial plantations, most of the Venezuelan territory comprises numerous landraces. Hence, due to the lack of national varieties and despite the huge, but unexploited variability of guava germplasm, we sampled guava landraces across the country and characterized them using 23 UPOV descriptors. Guava landraces were collected in an altitude gradient ranging from 0 to 2000 m.a.s.l. and in a variety of ecosystems, the vast majority of them associated with human settlements. The 100 collected samples were evaluated by phenotypic markers, and revealed an elevated degree of polymorphism. The most informative markers, based on the degree of variability, were those related to fruit characters: number of seeds and color of the skin and the flesh. The analyses also revealed a distribution pattern apparently related with certain regions of the country that show more abundance and/or more diversity of phenotypes. This may be related to the reproductive biology of P. guajava (selfing or outcrossing), its biotic and environmental interactions, and anthropic factors. The collected guavas with their broad variability constitute a valuable germplasm resource for the development of genetic improvement programs. Likewise, the variety of phenotypes and their geographical distribution suggest that the north of South America might represent the centre of origin of guava; however, this finding requires confirmation through a detailed and comprehensive phylogenetic analysis employing traditional and molecular biology tools.

ON THE CULTIVATION OF GUAVA IN VENEZUELA

Both autochthonous and introduced fruit crops exploitation in Venezuela have suffered from a common history of neglect, and few moments of accomplishment. Although fruit utilization is a customary nutritional habit of Venezuela's inhabitants well before the pre-Columbian times, currently, the per capita consumption of fruits in the country lags slightly below the recommended daily intake. Most of the efforts put into place regarding fruit culture in Venezuela have been mostly devoted to pathogen analysis and control; biotechnological advances have been almost inexistent, other than the development of in vitro tissue culture protocols, and a very poor analysis of the guava germplasm present in the country. In this short report data on guava production, varieties, cultural practices, ethno-botanical aspects, as well as main pathogens and pests of the crop, will be presented. Some efforts, however, look promising since some institutions (remarkably, Universidad de Los Andes, through the GUAVAMAP project, and Universidad del Zulia, with its long tradition in the fields of phytopathology and agronomical sciences) are investing important financial and human resources to catalog the diversity of Venezuelan guavas, and in the molecular and phenotypical characterization of guava landraces all over the country and the remnants of the first introduced varieties commercially exploited in western Venezuela.

SIMPLE SEQUENCE REPEATS (SSRS) FOR DIVERSITY CHARACTERIZATION OF GUAVA (PSIDIUM GUAJAVA L.)

Guava (Psidium guajava L.) is one of the economically most important fruit trees of the Myrtaceae. Until nowadays, guava breeding programs in Cuba have been limited to the selection and introduction of genotypes with important agronomic characteristics, but focussed studies on genetic diversity which is very important for the identification of potential parents for breeding programs, had not been undertaken. The utilization of microsatellite (SSR) markers for guava germplasm characterization and gene bank management was the main objective of this work. A total of 34 different SSR alleles ranging from three to seven per locus were detected in the examined genotypes with an average number of putative alleles per locus of 4.57. Out of these, twenty-four alleles were classified as common alleles, out of which 10 were widespread and 14 sporadic. Ten alleles were classified as rare, from which 7 were sporadic and 3 localised. For all SSR loci, a major number of homozygote genotypes were identified, except for the SSR locus mPgCIR09. This result reflected the medium to low levels of heterozygosis detected, which ranged from 0.08 to 0.54 with 0.38 as the total average for this parameter. Genotypes showing cultivar-specific markers were 'Dario 19-2'; 'Belic L-98'; 'BG 76-23'; 'Belic L-205' and 'Microguayaba'. These could be important materials for conservation purposes. The high number of common alleles detected suggested that most of the plant material analyzed shares a common genetic ancestor. The microsatellites evaluated could play an important role in the identification of guava accessions representing an interesting gene pool for ex situ maintenance.

COMPARISON OF THE POLYMORPHISM LEVEL, DISCRIMINATING CAPACITY AND INFORMATIVENESS OF MORPHO-AGRONOMIC TRAITS AND MOLECULAR MARKERS IN GUAVA (PSIDIUM GUAJAVA L.)

Agro-morphologic traits and molecular markers were compared in terms of their polymorphism level, discriminating power, and informativeness for 23 genotypes assembled in the Cuban guava germplasm collection. AFLP and SSR markers were powerful techniques for guava discrimination and variety identification, but the high level of polymorphic loci detected by the dominant AFLP marker highlights the discriminating capacity of this genetic marker. With a single AFLP primer combination all of the individuals were identified, while only a few genotypes can be differentiated with a single SSR primer combination or by morphological variables. The higher values of expected heterozygosity were detected by SSR. This value doubled the one obtained with AFLP, and reflects the high level of informativeness of this marker, due to the multiallelic and co-dominant nature of SSR; which makes them suitable for diversity studies. The morphologic diversity index provided a good estimate of diversity among guava accessions when phenotypic traits of high heritability were used, and it was comparable with the expected heterozygosity scored with DNA markers. The value of this index was the lowest. The assay efficiency index (A i ) and marker index (MI) had the same pattern of variation than discrimination capacity (D), number of banding pattern (I), number of unique banding pattern (I u ) and number of effective pattern (P) for both molecular markers. Then, these indexes are probably indicators of the discriminating capacity in guava.

ROOT GROWTH AND DEVELOPMENT OF 'CAS' GUAVA (PSIDIUM FRIEDRICHSTHALIANUM BERG-NIED.) SEEDLINGS DURING NURSERY STAGE

A root growth analysis for 'Cas' guava (Psidium friedrichsthalianum Berg-Nied.) seedlings was established. Seeds were extracted from ripe and healthy fruit harvested at the guava germplasm bank of Centro Fruticola of Zulia, Venezuela (11°00'00 LN, 71°30'00 LW). Seeds were sown in a seedbed that contained sterilized substrate. Seedlings were transferred into bags when they were about eight cm in height. Seedlings were grown in five or ten kilogram polyethylene bags containing three mixtures (1:1, 1:2 and 2:1) of soil and goat manure as substrates. Sampling was done monthly during six months. The variables measured for root growth were main root length, root fresh and dry mass, volume, and area. Treatments were arranged in a factorial, completely randomized design with five replicates. Data were statistically analyzed utilizing the SAS software. SigmaPlot of Jandel Scientific was applied to select the curvilinear regression model that best fitted the results. The model used to adjust the curves was y= a/1+e -(x-xo/b) . The equations that represent root volume growth for the proportions 1:1, 1:2 and 2:1 were: y= 9.310e+0/1+e -(x-1.335e+2/2.404e+1) R 2 =0.94; y= 1.281e+1/1+e -(x-1.379e+2/2,981e+1) R 2 =0.95 and y=9.659e+3/1+e -(x-5.119+2/4.894e+1) R 2 =0.95, respectively. Bag size and soil:goat manure proportions are related with time during nursery stage. Ten kilogram bags and the 1:2 mixtures were appropriate for good root growth and development during six months in the nursery.

EVALUATION OF MEXICAN GUAVA GERMPLASM AGAINST ROOT KNOT NEMATODES

Root knot nematodes (Meloidogyne spp.) are one of the main phytosanitary problems of guava orchards in Mexico. At Calvillo, Aguascalientes, almost 90% of the seven-thousand hectares cultivated with guava are infested with nematodes. Although there are chemical and biological strategies to manage this problem, genetic resistance of native guava germplasm under cultivation has never been studied. The purpose of the present study was to determine the degree of susceptibility of a group of guava selections included at the germplasm bank of INIFAP as well as other guava accessions. Air-layering plants of the selections 10, 12, 20, 45, 46, 48, 106, 115, 117, and 118 were obtained, and then placed in pots of 12 kg of capacity. Plants were inoculated with 12 ml J2 plus nematode eggs collected at infested guava orchards of Aguascalientes, Michoacan, and Zacatecas. Results using air-layering plants showed that selections 46, 106, and 45 were more tolerant with 26, 35, and 35% of root damaged, respectively, while the most susceptible was selection 48 with 70% of the roots showing galls. In the group of guava seedlings, four accessions (51, 58, Boyaca, and Brazil) showed the highest gall numbers per centimeter of root, whereas the least affected were selection 42 and a Psidium spp. This study provides evidence that guava genetic resistance to nematodes could be present in the germplasm under study, and could be used as rootstocks or hybridization in future works.

Morphological and genetic diversity of Mexican guava germplasm

Fifty morphological characteristics, fruit production over 3 years (from 1999 to 2002) and the amplified fragment length polymorphism (AFLP) technique were used to analyse a set of 48 guava (Psidium guajavaL.) accessions cultivated in Mexico, in order to characterize their genetic relationships. Germplasm was collected from the Calvillo-Cañones region and planted in Huanusco, Mexico. The study included twoP. cattleianum(Sabine) and twoP. friedrichsthalianum(Berg-Niedenzu) accessions from Costa Rica as outgroups. Principal component analysis (PCA) explained less than 30% of total variation and 14 characteristics from trees (1), leaves (2) and fruits (11) were the most informative. PCA analysis separated the germplasm into three major groups of accessions based on fruit size and weight, stem diameter and leaf size. Significant differences in fruit yield were detected among accessions and years, whereP.guajavaproduced 36 kg/year/tree of fresh fruit whileP. cattleianumandP. friedrichsthalianumshowed fruit yield lower than 7 kg/year/tree. The fruit yield broad sense heritability was 0.25. The AFLP analysis produced two clusters ofPsidiumaccessions, the first includedP. cattleianumandP. friedrichsthalianum, and the secondP. guajavaaccessions. This is the first report about the use of AFLP marker methodology for the genetic characterization of Mexican native guava germplasm and the results based on phenotypic and productive characteristics suggest that germplasm was selected from open pollinated trees.

Studies on Quantitative Characteristics of Fruits of Some Guava Germplasm in Both on and Off-Seasons

Studies on Quantitative Characteristics of Fruits of Some Guava Germplasm in Both on and Off-Seasons