Methods of inoculation and evaluation of Erwinia psidii in eucalypt

The dieback and wilting caused by Erwinia psidii are emerging eucalypt diseases that have been observed since 2014 in the south and central‐south regions of Brazil. Field observations have shown variability in disease severity resistance among Eucalyptus spp. clones and species. It is hypothesized that this variability is due to genetic resistance. To confirm this hypothesis, inoculations in genetically distinct eucalypt plants are necessary. However, lack of an inoculation method and disease assessment makes difficult to select resistant genotypes for use in commercial plantations or genetic breeding programmes. Three inoculation methods were tested on eight clones of Eucalyptus spp. Among them, inoculum deposition with bacteria‐impregnated toothpick on the axillary buds was the simplest and most effective, capable to reproduce the disease symptoms observed under conditions of natural infection. We also developed a rating scale for disease assessment. Among eight clones tested, only Clone 1 (Eucalyptus saligna) and Clone 2 (Eucalyptus urophylla) were resistant.     

Wilt and die‐back of Eucalyptus spp. caused by Erwinia psidii in Brazil

A new disease of unknown bacterial aetiology has been observed in eucalyptus stands since 2009. It is characterized by die‐back, wilting and lesions on the branches, petiole and midrib in association with macroscopic and microscopic bacterial ooze. To date, this disease has been observed in stands of clonal Eucalyptus saligna, E. grandis and E. urophylla x E. grandis hybrids and in E. dunnii seedling plantations in the states of São Paulo, Rio Grande do Sul and Mato Grosso do Sul. Considering the economic importance of eucalyptus plantations and the potential losses caused by this disease, this study aimed to identify and characterize the causal agent. Thirty‐four strains were obtained from infected plants, which were collected in the field from four locations. The inoculation of detached leaves and intact rooted cuttings supported pathogenicity in eucalyptus. The phylogenetic analysis of four housekeeping genes (16S rDNA, gapA, recA and rpoB) as well as biochemical tests confirmed the identity of strains belonging to the species Erwinia psidii. This is the first report of E. psidii as the cause of wilt and die‐back in Eucalyptus spp. in Brazil.     

Multi-level characterization of perennial cotton (Gossypium hirsutum L. race marie-galante Hutch.) populations from the northeastern Brazil to the breeding and conservation of this germplasm

Genetic Resources and Crop Evolution - The remaining populations of perennial cotton (Gossypium hirsutum L. r. marie-galante Hutch.) that occur in northeastern Brazil are part of the primary gene...     

Flow rate sprinkler development for site-specific irrigation

Due to the rapid depletion of water resources, water must be used more efficiently in agriculture to maintain current levels of yield in irrigated areas. The efficiency of irrigation systems can be increased by adjusting the amount of water applied to specific conditions of soil and crop, which may vary in a field. Taking into account spatial and temporal variability, it is evident that an equipment capable of providing different irrigation levels is necessary to meet the water requirement of the soil. This work aims to develop and evaluate a flow rate sprinkler to be used in center pivots or linear moving irrigation systems, with potential for utilization in irrigation scheduling. A prototype was developed by duplicating its calibrations, and discharge coefficient adjustment was carried out in the laboratory. To predict the flow rate, a successful model that represented the operation of the flow rate sprinkler was established. The calibration of the flow rate sprinkler prototype showed satisfactory statistical and technical results. Automation of the prototype was achieved by driving a step motor using communication from the parallel port of a microcomputer, which was controlled by a software developed for this purpose. The results were satisfactory and technically feasible.     

Characterization of the microtube emitters used in a novel micro-sprinkler

The microtube is a simple and cheap emitter that was widely used throughout the world in the early days of drip irrigation. Its length can be adjusted according to the pressure distribution along the lateral line and the discharge from the microtube can be adjusted by its length. This not only counters the pressure loss due to pipe friction but also makes it suitable for undulating and hilly conditions, where pressure in the lateral line varies considerably according to the differences in elevation. This is the major problem facing the designer, i.e., emitter flow changes as the acting pressure head changes. In this study, a novel micro-sprinkler system is proposed that uses microtube as the emitter and where the length of the microtube can be varied in response to pressure changes along the lateral to give uniformity of emitter discharges. The objective of this work is to develop and validate empirical and semi-theoretical equations for the emitter hydraulics. Laboratory testing of two microtube emitters of different diameter over a range of pressures and discharges was used in the development of the equations relating pressure and discharge, and pressure and length for these emitters. The equations proposed will be used in the design of the micro-sprinkler system, to determine the length of microtube required to give the nominal discharge for any given pressure. The semi-theoretical approach underlined the importance of accurate measurements of the microtube diameter and the uncertainty in the estimation of the friction factor for these tubes.     

Storability of ‘Conference’ Pear Under Various Controlled Atmospheres

In two consecutive experimental seasons it was investigated the storage capacity of ‘Conference’ pear (Pyrus communis, L.) under regular air (RA) and various controlled atmosphere (CA) conditions during six months at 0?°C (±0.3). The occurrence flesh browning (FB), core browning (CB) and cavity formation (CF) was evaluated at each 2?months storage intervals and the ripening quality traits analyzed immediately at the end of storage period and after 7 days of shelf-life in air at 20?°C. The storage conditions were: RA; 0.5?kPa O₂?+?0.5?kPa CO₂; 1.5?kPa O₂?+?1.5?kPa CO₂, 2.0?kPa O₂?+?1.0?kPa CO₂; 3.0?kPa O₂?+?6.0?kPa CO₂ and 0.5?kPa O₂?+?6.0?kPa CO₂. After six months, ‘Conference’ pear was very susceptible to FB, CB and CF under CA-storage. The damages started to develop at the second month of storage, increasing continuously until end of storage period. At storage end, pear fruits kept under 0.5?kPa O₂?+?6.0?kPa CO₂ showed a dramatic high occurrence of FB, CB and CF with a severity index of 50.6, 45.3 and 27.1, respectively. The lowest incidences of FB, CB and CF were scored in fruits kept at 2.0?kPa O₂?+?1.0?kPa CO₂ with severity indexes of 1.1, 1.1 and 1.0, respectively. Flesh firmness, skin color, titratable acidity and total soluble solids were satisfactory under 2.0?kPa O₂?+?1.0?kPa CO₂. In conclusion, ‘Conference’ pear cannot be stored under O₂ partial pressure lower than 2.0?kPa and CO₂ higher than 0.5?kPa.