Few genetic markers are available in Musa spp. as a result of a lack of inheritance studies. Full-sib diploid (2n = 2x = 22) plantain-banana hybrids of the International Institute of Tropical Agriculture were selfed or outcrossed with other diploid bananas, one of which is an improved selection from Central America. Three populations having albinos (complete lack of chlorophyll in any plant tissue) were produced. The segregation ratios for albinism suggested that this deleterious trait is controlled by one or two recessive alleles. The small sample sizes (a problem inherent in the low reproductive fertility of cultivated parthenocarpic Musa) in two of these three populations did not allow for conclusiveness between the one or two genes model. However, a distinction was possible with the third population, consisting of 64 seedlings, of which four were albinos. The segregation ratio for albinism fit the 15:1 ratio (χ2 = 0.07, P = 0.79) and not the 3:1 ratio (χ2 = 11.02, P < 0.01), suggesting that albinism in Musa spp. is under the genetic control of at least two independent recessive alleles with complementary gene action. This finding also demonstrates that deleterious recessive alleles are present in the cultivated AAB plantain gene pool and in cultivated and advanced AA banana breeding populations. The latter suggests that population improvement through phenotypic recurrent selection for agronomic traits might be based on the elimination of deleterious recessive genes.
Rodomiro Ortiz and Dirk R. Vuylsteke
Dirk R. Vuylsteke and Rodomiro Ortiz
In vitro-propagated plants of plantain (Musa spp., AAB group) did not manifest consistently superior horticultural performance compared to conventional propagules. Tissue culture plants grew vigorously and taller than sucker-propagated plants, but higher yield was not obtained, probably because of severe disease and suboptimal husbandry input. Phenotypic variation was higher in tissue culture plants, although this increase was not always statistically significant. There were no other detrimental effects of in vitro propagation on field performance. Botanical seed set rates for the two types of propagules were similar. The advantages of tissue-culture-derived plants as improved planting material would be most relevant for establishing field nurseries for further clean, conventional propagation of newly bred or selected genotypes.
Rodomiro Ortiz and Dirk R. Vuylsteke
Apical dominance, i.e., the inhibition of lateral bud growth due to growth substances released by the terminal bud, has been considered as a limiting factor for the perennial productivity of plantains (Musa spp., AAB group). Segregation ratios in F1 and F2 plantain-banana hybrids suggest that inheritance of apical dominance is controlled by a major recessive gene, ad. The dominant Ad allele improved the suckering of plantain-banana hybrids, as measured by the height of the tallest sucker at flowering and harvest. At harvest, the ratoon crop of the diploid and tetraploid hybrids had completed 70% to 100% of its vegetative development, whereas the ratoon of the plantain parents, due to high apical dominance, was only at 50% of total pseudostem growth. Sucker growth rates are generally the result of gibberellic acid (GA3) levels, and it is suggested that the Ad gene regulates GA3 production. However, the Ad gene has incomplete penetrance, genetic specificity, and variable expressivity. Increased frequency of the Ad gene and a commensurate improvement in the suckering behavior of the diploid populations may be achieved by phenotypic recurrent selection.
Alvaro del Cid, Ramiro Ortiz, and H.R. Valenzuela
PRECODEPA was formed with the purpose of coordinating research and extension to improve small-farm potato production. The program involves 9 countries in North, Central America and the Caribbean with the cooperation of the International Potato Center (CIP). Research and extension work was planed based on identified bottlenecks. Work was coordinated when similar bottlenecks were identified in different regions and/or countries. The project strategies emphasized the following: training of personnel to coordinate the work between extension and research; development of integrated pest management (IPM) practices; technology generation and validation trials on farmers' fields, and market development for commercialization purposes. The success of this unique program should serve as a model for similar agricultural projects in the future.
A. Tenkouano, D. Vuylsteke, J. Okoro, D. Makumbi, R. Swennen, and R. Ortiz
José R. Bautista-Aguilar, Lourdes G. Iglesias-Andreu, Jaime Martínez-Castillo, Marco A. Ramírez-Mosqueda, and Matilde M. Ortiz-García
Vanilla planifolia Jacks. is a species of great economic importance, since vanillin, a compound highly valued in the food and pharmaceutical industry, is extracted from its pods. This species is in the category of special protection, so it is important to take actions for its conservation and to maintain the genetic stability of the conserved germplasm. An adequate way to achieve this is through the minimal growth in vitro conservation techniques. The present work aimed to establish an in vitro conservation protocol for vanilla germplasm that allows the genetic stability of the conserved material. For the establishment of the minimal growth in vitro conservation protocol: two concentrations of basal Murashige and Skoog (MS) medium (50% and 100%), two incubation temperatures (4 and 22 °C) and two concentrations of abscisic acid (ABA) (3 and 5 mg⋅L−1) were evaluated. To evaluate the genetic stability of the germplasms used in this study (cultivated, wild, and V. insignis morphotypes) by analyzing the profiles of molecular markers SSR (simple sequence repeats) and ISSR (inter simple sequence repeats). The MS medium (100%) supplemented with 3 mg⋅L−1 of ABA and incubated at 22 °C, was the best treatment for the in vitro conservation of Vanilla spp. Compared with the control treatment, it allowed us to obtain smaller shoots (1.17 × 0.17 cm), which showed high genetic stability, given by the low percentages of polymorphism detected in morphotypes cultivated and wild (SSR 0%, ISSR 2%) and V. insignis (SSR 0%, ISSR 0%). We conclude the usefulness of the established protocol to conserve the genetic variation of the evaluated Vanilla germplasm.
Raúl De la Rosa, Angjelina Belaj, Antonio Muñoz-Mérida, Oswaldo Trelles, Inmaculada Ortíz-Martín, Juan José González-Plaza, Victoriano Valpuesta, and Carmen R. Beuzón
In the present work, a set of eight new hexa-nucleotide simple sequence repeats (SSRs) is reported in olive (Olea europaea L). These SSRs loci were generated on the basis of expressed sequence tag (EST) sequences in the frame of an olive genomic project. The markers showed a high level of polymorphism when tested on a set of cultivars used as genitors in the olive breeding program of Córdoba, Spain. The long-core repeat motif of these markers allows a wider separation among alleles, thus permitting an accurate genotyping. Besides, these markers showed comparable levels of polymorphism to di-nucleotide SSRs, the only ones so far reported in olive. Selected on the basis of their discrimination capacity, four of the eight SSRs were used to test their ability for paternity testing in a total of 81 seedlings coming from 12 crosses. The paternity testing showed that seven crosses matched the alleged paternity and the remaining five were products of illicit pollinations. These results exactly matched with previous paternity testing performed with di-nucleotide SSR markers. These results demonstrate the usefulness of the developed hexa-nucleotide repeated motifs for checking the paternity of breeding progenies and suggest their use on variability studies.