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-The variability in the chronology of the vegetative and reproductive development of weedy rice complex has been little studied. However, a field trial was established to study the timing of growth stages of sixteen weedy rice morphotypes and five rice varieties of Costa Rica. Weedy rice presented a wide range of variation for all descriptors among and within morphotypes. Weedy rice was taller than the rice varieties during vegetative phase and showed a growth increase of 14-23 cm every two weeks. Six morphotypes emerged earlier than commercial rice varieties, but no differences where found between samples for the time required for starting tillering. Early emergence of weedy rice morphotypes was not associated with early flowering, thus no correlation was detected between the vegetative and reproductive phases. All weedy rice morphotypes reached anthesis and maturity earlier than the rice varieties. Nevertheless, varieties Setesa-9 and CR-5272 overlapped anthesis with eleven morphotypes and variety CR-4338 overlapped flowering with eight weedy rice morphotypes. In contrast, none of the morphotypes overlapped anthesis with varieties CR-1821 and CR-1113. The results obtained showed the competitive capacity of weedy rice and provided valuable information about flowering overlap between weedy rice morphotypes and rice varieties which will be useful in the design of gene flow studies among them.Keywords: anthesis overlapping; growth stages; red rice; rice varieties. RESUMO -O desenvolvimento vegetativo e reprodutivo das diferentes variantes morfológicas do arroz-vermelho tem sido pouco estudado. Um ensaio de campo com dezesseis morfotipos de arroz-vermelho e cinco variedades comerciais de arroz da Costa Rica foi estabelecido com o fim de estudar o crescimento dessa planta daninha. Nos resultados, observou-se que o arroz-vermelho

Herbicide-resistant rice cultivars allow selective weed control. A glufosinate indica rice has been developed locally. However, there is concern about weedy rice becoming herbicide resistant through gene flow. Therefore, assessment of gene flow from indica rice cultivars to weedy rice is crucial in Tropical America. A field trial mimicking crop-weed growing patterns was established to assess the rate of hybridization between a Costa Rican glufosinate-resistant rice line (PPT-R) and 58 weedy rice accessions belonging to six weedy rice morphotypes. The effects of overlapping anthesis, morphotype, weedy accession/PPT-R percentage, and the particular weedy accession on hybridization rates were evaluated. Weedy rice accessions with short overlapping anthesis (4-9 days) had lower average hybridization rates (0.1%) than long anthesis overlapping (10-14 days) accessions (0.3%). Hybridization also varied according to weedy rice morphotype and accession. Sativa-like morphotypes (WM-020, WM-120) hybridized more readily than intermediate (WM-023, WM-073, WM-121) and rufipogon-like (WM-329) morphotypes. No hybrids were identified in 11 of the 58 accessions analyzed, 21 accessions had hybridization rates from 0.01% to 0.09%, 21 had rates from 0.1% to 0.9%, and 5 had frequencies from 1% to 2.3%. Another field trial was established to compare the weedy rice-PPT-R F(1) hybrids with their parental lines under noncompetitive conditions. F(1) hybrids had a greater phenotypic variation. They had positive heterosis for vegetative trait and reproductive potential (number of spikelets and panicle length) traits, but negative heterosis for seed set. This study demonstrated the complexity of factors affecting hybridization rates in Tropical America and suggested that the phenotype of F(1) hybrids facilitate their identification in the rice fields.

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Wild crop relatives are an important source of genetic diversity for crop improvement. Diversity estimates are generally lacking for many wild crop relatives. The objective of the present study was to analyze how genetic diversity is distributed within and among populations of the wild rice species Oryza glumaepatula in Costa Rica. We also evaluated the likelihood of gene flow between wild and commercial rice species because the latter is commonly sympatric with wild rice populations. Introgression may change wild species by incorporating alleles from domesticated species, increasing the risk of losing original variation. Specimens from all known O. glumaepatula populations in Costa Rica were analyzed with 444 AFLP markers to characterize genetic diversity and structure. We also compared genetic diversity estimates between O. glumaepatula specimens and O. sativa commercial rice. Our results showed that O. glumaepatula populations in Costa Rica have moderately high levels of genetic diversity, comparable to those found in South American populations. Despite the restricted distribution of this species in Costa Rica, populations are fairly large, reducing the effects of drift on genetic diversity. We found a dismissible but significant structure (θ = 0.02 ± 0.001) among populations. A Bayesian structure analysis suggested that some individuals share a significant proportion of their genomes with O. sativa. These results suggest that gene flow from cultivated O. sativa populations may have occurred in the recent past. These results expose an important biohazard: recurrent hybridization may reduce the genetic diversity of this wild rice species. Introgression may transfer commercial traits into O. glumaepatula, which in turn could alter genetic diversity and increase the likelihood of local extinction. These results have important implications for in situ conservation strategies of the only wild populations of O. glumaepatula in Costa Rica.

The Adapting Agriculture to Climate Change Project set out to improve the diversity, quantity, and accessibility of germplasm collections of crop wild relatives (CWR). Between 2013 and 2018, partners in 25 countries, heirs to the globetrotting legacy of Nikolai Vavilov, undertook seed collecting expeditions targeting CWR of 28 crops of global significance for agriculture. Here, we describe the implementation of the 25 national collecting programs and present the key results. A total of 4587 unique seed samples from at least 355 CWR taxa were collected, conserved ex situ, safety duplicated in national and international genebanks, and made available through the Multilateral System (MLS) of the International Treaty on Plant Genetic Resources for Food and Agriculture (Plant Treaty). Collections of CWR were made for all 28 targeted crops. Potato and eggplant were the most collected genepools, although the greatest number of primary genepool collections were made for rice. Overall, alfalfa, Bambara groundnut, grass pea and wheat were the genepools for which targets were best achieved. Several of the newly collected samples have already been used in pre-breeding programs to adapt crops to future challenges.

This review discusses a multidisciplinary and multicomponent approach leading to the development and commercial release of transgenic Costa Rican rice varieties tolerant to the herbicide gluphosinate ammonium. We describe the field evaluations of the transgenic lines and their potential environmental impact, focusing on gene flow, particularly in relation to native wild Oryza species and weedy rice, based on trials performed in compliance with the national regulatory requirements of the country. We also present a socio-economic analysis of rice production in Costa Rica and the economic benefits of genetically modified (GM) rice as well as an environmental risk-benefit analysis for the deployment of GM rice. Additionally, food safety evaluation, intellectual property management, requirements for deregulation, and options for the commercialization of the new varieties are discussed. We also present results from a national survey aimed at assessing the level of support for GM crops in Costa Rica as this forms an integral component of our approach. Taken together, our results demonstrate that the adoption of these genetically improved rice varieties will provide clear benefits to Costa Rican rice growers and consumers.