Strategy for The Transition Towards Conservation Agriculture Practices in Rice Cultivation Systems in Cuba

Cuban agriculture to achieve the sustainability of agricultural systems needs to initiate a transition process towards conservation agriculture practices, which implies a change in production systems and the technologies they use. Rice (Oryza sativa L.) is considered a staple food for more than half of the world's population. However, the adverse effects of climate change, together with soil degradation and the scarcity of irrigation water threaten the sustainability of rice production under irrigated conditions [1, 2]. Intensive tillage practices have been shown to increase environmental pollution, deteriorate the soil and involve high water consumption [3, 4]. Therefore, conservation agriculture (CA) practices have been recommended to conserve resources and increase ecosystem services [2, 5]. The CA is an agricultural system that is characterized by the interrelation of three fundamental principles: to keep the soil permanently covered with crop residues or plant covers at least 30%, a minimum disturbance of the land and diversification of the species cultivated in rotation [6]. Some 140 thousand hectares of rice are planted in Cuba [7-9]. However, the low yields obtained require the importation of 400,000 tons of rice annually. A roadmap for the transition towards CA practices was recently adopted as the country's policy. But the current conditions of rice soils (characterized by low organic matter content, compaction and poor drainage), subjected to intensive (traditional) tillage practices for long periods of time (between 30 and 50 years), put at risk the implementation of the basic principles of CA and its adoption as an accepted practice by farmers.

Antagonistic Potential of Soil Streptomyces Isolates from Southern Thailand to Inhibit Foodborne Bacterial Pathogens

Streptomyces are well known for their competence to produce thousands of bioactive secondary metabolites and enzymes. This study aimed to assess the inhibitory activities of crude extracts from diverse Streptomyces collected from rice soils in Narathiwat, Thailand, against foodborne bacterial pathogens. In total, 136 Actinomycete isolates were screened using a cross-streak method for the ability to produce effective metabolites against 5 pathogenic bacteria. Out of these, 19 (13.97%) isolates had antibacterial activity against at least one tested bacterium. Most of the isolates could strongly suppress the growth of S. aureus ATCC25923 and B. cereus MTCC430 except P. aeruginosa ATCC27853. On the basis of morphological, cultural, and biochemical characteristics, all potent isolates exhibited typical features that fitted the genus Streptomyces. Two of the 7 selected ethyl acetate crude extracts had good antagonistic activity against S. aureus ATCC25923 and B. cereus MTCC430 when tested using the agar well diffusion assay. Furthermore, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of the 2 extracts evaluated using the colorimetric broth microdilution method ranged from 256 to >1,024 μg/ml against the tested bacteria. The partial nucleotide sequences of the 16S rRNA gene led to identifying both active isolates as Streptomyces species. These active Streptomyces isolates could provide an interesting source for generating innumerable natural compounds with antibacterial activity that can presumably be developed to fight bacterial pathogens in the near future.

Parametric and Non-Parametric Suitability Evaluations of Rice Soils of Asu River Group Parent Materials in Ohaozara, Nigeria

The study was carried out in Ohaozara Southern Ebonyi State in Southeastern Nigeria. Study area was identified in a rice soil of about 120 hectares used for FGN/IFAD Value Chain Development program (VCDP). Three profile pits were dug on a transect line of about 100 – 200m apart for suitability evaluation study. The aim of the study was to use parametric and non – parametric suitability evaluation to study the rice soils under Asu River Group parent material. Parametric method is where each limiting characteristic was rated using information provided on factor ratings of land use requirements for wetland ricetable. In Nonparametric method, pedons were placed in suitability classes by matching their land characteristics with the agronomic requirements of rice. The index of productivity (IP) (actual and potential) was calculated using the equation: IP= A x √(B/100 x C/100 x D/100xE/100). Suitability evaluation results show that climate, soil physical conditions and wetness were optimum S1(95%) and moderately suitable S2(85%) while,fertility and toxicity parameters made the soil marginally suitable S3(60%). Parametric and non – parametric suitability evaluation revealed that the soils were mostly marginally suitable both potentially and currently. Major limitations of the investigated soils bother on fertility and Al toxicity.

Evaluation of the production of antifungal metabolites against Colletotrichum gloeosporioides in Streptomyces 5.1 by random mutagenesis

Streptomyces 5.1 is a bacterium isolated from rice soils in the south of the Tolima department (Colombia). This microorganism is characterized by its antagonistic activity against rubber tree phytopathogens like Colletotrichum gloeosporioides, the causal agent of leaf anthracnose. The antifungal activity of this Streptomyces isolate has been associated with secondary metabolites production. However, the identity of those metabolites is unknown because its purification and identification have not been possible through classic chemical studies. Therefore, aiming to contribute in the study of the secondary metabolites produced by 5.1 from a molecular approach, this research seeks to identify -preliminarily- the genomic fingerprint changes associated with the production of antifungal secondary metabolites produced by Streptomyces 5.1 through the evaluation of a mutant library of 5.1 obtained by random mutagenesis using controlled ultraviolet light exposure. The antifungal activity of obtained mutants was evaluated using Colletotrichum gloeosporioides (C1) fungus as a biosensor, isolated by the Biotechnology Institute of Universidad Nacional de Colombia. In this way, the library of mutants of 5.1, initially formed by 300 isolations, was classified into two phenotypic groups of interest: enhanced mutants (1 isolate) and null mutants (11 isolates) of secondary metabolites. The genomic changes in both groups were analyzed by obtaining the genomic profile of the isolates using Repetitive Extragenic Palindromic (Rep-PCR). The obtained profiles evidenced the presence of one additional band in the enhanced mutant, and the absence of a specific band in the non-producing mutants, both in comparison with the original strain. These bands are proposed for a future sequencing study which will define their role in the production process of metabolites with antifungal activity in Streptomyces 5.1.

Multiple Small-Effect Alleles of Indica Origin Enhance High Iron-Associated Stress Tolerance in Rice Under Field Conditions in West Africa

Understanding the genetics of field-based tolerance to high iron-associated (HIA) stress in rice can accelerate the development of new varieties with enhanced yield performance in West African lowland ecosystems. To date, few field-based studies have been undertaken to rigorously evaluate rice yield performance under HIA stress conditions. In this study, two NERICA × O. sativa bi-parental rice populations and one O.sativa diversity panel consisting of 296 rice accessions were evaluated for grain yield and leaf bronzing symptoms over multiple years in four West African HIA stress and control sites. Mapping of these traits identified a large number of QTLs and single nucleotide polymorphisms (SNPs) associated with stress tolerance in the field. Favorable alleles associated with tolerance to high levels of iron in anaerobic rice soils were rare and almost exclusively derived from the indica subpopulation, including the most favorable alleles identified in NERICA varieties. These findings highlight the complex genetic architecture underlying rice response to HIA stress and suggest that a recurrent selection program focusing on an expanded indica genepool could be productively used in combination with genomic selection to increase the efficiency of selection in breeding programs designed to enhance tolerance to this prevalent abiotic stress in West Africa.

Soil fertility evaluation of rice soils of Lumbajong block of Karbi Anglong district under hill zone of Assam through nutrient indexing

The Lumbajong block of Karbi Anglong district of Assam is characterized by undulating topography comprising of hillocks and lowland paddy fields. Cultivation of rice in traditional ways for years without adequate and balanced use of chemical fertilizers and with little or no use of organic manure have caused severe fertility deterioration resulting in stagnating or even declining productivity of the paddy field soils. Spatial distributions for organic carbon, available N, available P and available K were examined in the soil samples of selected rice fields in 102 different locations covering six villages in the block to evaluate the fertility status of the block. The study revealed that there is much variation in soil fertility status of soils developed on various land forms in the area as the soils were having low to high in organic carbon (0.42 to1.12 %), low to medium in available nitrogen (175.62 to 376 kg/ha) content; low in available P (3.86 to 28.29 kg/ha) and low to high in available K (71.68 – 439.04 kg/ha) contents. The soils of Lumbajong block were characterized as medium-medium-low-medium (MMLM) category based on the nutrient index calculated with respect to organic carbon, available N, available P and available K.