Physical and visual properties of grape rachis as affected by water vapor pressure deficit

Rachis browning of table grapes after harvest is a significant problem, and water loss is considered the primary factor in browning. The major rachis desiccation and browning occurs during marketing at ambient temperatures and relative humidity (RH) which create high water vapor pressure deficits (WVPD). In this study the effect of WVPD and its components on rachis browning were examined on the two white seedless cultivars ‘Superior’ and ‘Thompson’. The grape clusters were stored at 20 °C or at 10 °C with low (70%) or high (>95%) RH, thus creating 4 WVPD levels. At each WVPD the clusters were held in open punnets, punnets sealed with low density polyethylene film or microperforated polyethylene, and examed every 2 or 3 d for weight loss, berry firmness, rachis dry weight and subjective rachis index. In addition, the rachis were photographed and image analysis employed to identify the level of browning. The results show that image analysis gave very similar patterns to subjective evaluation of rachis browning with correlation coefficients up to 0.90. However, image analysis detected an increase in browning before subjective evaluation. There was poor overall correlation between cluster weight loss and rachis dry weight to browning for ‘Superior’ grapes but a good correlation for ‘Thompson’. Rachis of ‘Superior’ suffered extensive browning at 20 °C even at high RH while rachis of ‘Thompson’ remained relatively green under similar conditions. ‘Thompson’ grape rachis remained green during the entire examination period (11 d) when held at high RH in either 10 °C or 20 °C. At high WVPD, microperforated packaging offered better control of browning in ‘Superior’ grapes than closed packaging, while clusters of ‘Thompson’ retained green rachis after 4 d in open punnets, and after 7 d in covered punnets. In summary, detailed analysis of rachis browning shows that water loss is an important but not the only factor in browning. Quantitative and objective measurement of rachis browning is likely to facilitate better communication of experimental data and higher resolution of processes which lead to browning.     

Conservation agriculture as a sustainable option for the central Mexican highlands

Tropical highlands of the world are densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen all over this agro-ecological zone. Based on selected soil quality indicators, i.e. time-to-pond, aggregate distribution and stability (expressed as the mean weight diameter (MWD) for dry and wet sieving, respectively) and soil moisture, from a representative long-term sustainability trial initiated in 1991 in Central Mexico (2240 masl; 19.31°N, 98.50°W; Cumulic Phaeozem), some insights into the feasibility of conservation agriculture (CA) as part of a sustainable production system in the tropical highlands are given. Zero tillage plots with crop residue removal showed low aggregate distribution (average MWD = 1.34 mm) and stability (average MWD = 0.99 mm) resulting in top layer slaking, increased erosion and low time-to-pond values. Retaining the residue in the field with zero tillage avoided the above-mentioned negative evolution for both aggregate distribution as stability (average MWD = 2.77 and 1.51 mm, respectively) and even improved the physical conditions of the soil as compared to conventional practice. Throughout the growing season the lowest soil moisture content was found in zero tillage without residue (average over the entire growing season = 20.5% volumetric moisture content), the highest in zero tillage with residue retention (average = 29.7%) while conventional tillage had intermediate soil moisture values (average = 27.4%). Zero tillage without residue retention had most days of soil moisture values under permanent wilting point, while zero tillage with residue retention had the least. Taking into account these results, zero tillage with residue retention can clearly be a part of an integrated watershed management scheme towards sustainable agriculture in the tropical highlands. It is clear that to develop new management practices to improve water use, reduce erosion and enhance human labor/animal power focus must be on the use of conservation agriculture both for rainfed as well as irrigated production systems and be fine tuned for each system.     

The efficacy of ultrasonic fumigation for disinfestation of storage facilities against postharvest pathogens

Inoculum of postharvest pathogens can accumulate inside storage rooms and contaminate new batches of fruit and vegetables, but this chain can be broken by disinfecting storage facilities between storage periods. Quaternary ammonium (QA) has been known for over 50 years as an efficient disinfectant against microorganisms, with wide applications in the food industry. The aim of this study was to determine the efficacy of didecyldimethylammonium chloride (Sporekill, designated here as QA^sk), against development of Botrytis cinerea after direct exposure or by ultrasonic fogging. Following direct exposure to a concentration of QA^sk below 5 mg L^?1, a population of 10⁴ conidia of B. cinerea was inactivated after 2 min; ultrasonic fogging with QA^sk at 500 mg L^?1 took 30 min to achieve consistent inactivation. Fumigation at 20 °C was considerably more effective than fumigation at 5 °C, and similar results were obtained for three other postharvest pathogens, Penicillium expansum, Colletotrichum gloeosporioides and Alternaria alternata. These results show that conidia of B. cinerea are highly sensitive to direct exposure to QA^sk, but that effective sanitation of a storage facility by ultrasonic fumigation requires a QA^sk concentration two orders of magnitude greater.     

Glucosinolates Determined by HPLC in the Seeds of Microspore-Derived Homozygous Lines of Rapeseed (Brassica napus L.)*

Microspore culture was employed to measure the relative efficiencies of anther culture and isolated microspore culture for the regeneration of embryoids and plants of Brassica napus. The yield of embryoids and plants was at least 10-fold greater from isolated microspores than from anther cultures. Approximately 1400 microspore-derived homozygous line's, the parental varieties and the corresponding F₂ plants were grown in a field trial. Important agricultural characteristics, such as morphological homogeneity, growth rate, onset of flowering and seed setting were evaluated subjectively and seed yield and glucosinolate content of individual plants were determined. The relative concentrations of up to S different glucosinolates in these seeds were measured via an automated high performance liquid chromatography (HPLC) system. The alkenyl and indole glucosinolates, the two most important categories of glucosinolates, were found in varying proportions and were independently determined in these line's. Our results do not support the previously suggested connection between low concentrations of glucosinolates and weak growth and/or poor seed yield. Additionally, no evidence was found that the lines derived from isolated microspore culture were subjected to unexpected selection pressures that might adversely affect the diversity of the lines obtained. These results demonstrate that microspore culture is a powerful tool not only for genetic analysis bur also for practical plant breeding.     

Acidified peel of litchi fruits selects for postharvestPenicillium decay

Litchi fruits are fumigated after harvest with sulfur dioxide (SO₂) to prevent their rapid browning. SO₂ blocks enzymatic activity but bleaches the fruits and, if this process is followed by dipping the fruit in dilute hydrochloric acid, the appealing red color is regained. Hot water brushing (HWB) is among the alternative methods that were developed to replace the use of SO₂. HWB reduced fungal population size on the surface of the fruit peel after treatment but did not eliminate fruit infection after storage. Whereas untreated fruits were infected with a variety of fungal species,Penicillium sp. was the only fungus that developed on the pericarp after storage in fruits that had been dipped in 1.5M HCl. Fruit treated by HWB followed by handling and storage under sterile conditions suffered greater decay than fruit stored under non-sterile conditions but with more ventilation. APenicillium sp. isolated from litchi grew well in liquid medium acidified to the pH range reported for SO₂ and HCl-treated litchi fruits. Morphological analysis identified fungal isolates asP. aurantiogriseum. Internal transcribed spacer sequence analysis of five isolates suggested a sequence similarity toP. commune. Our data support the hypothesis that dipping litchi fruit in hydrochloric acid eliminates infection by common opportunistic fungi and selects forPenicillium species that tolerate low pH. http://www.phytoparasitica.org posting April 30, 2004.     

High-resolution mapping of human chromosome 11 by in situ hybridization with cosmid clones

Cosmid clones containing human DNA inserts have been mapped on chromosome 11 by fluorescence in situ hybridization under conditions that suppress signal from repetitive DNA sequences. Thirteen known genes, one chromosome 11-specific DNA repeat, and 36 random clones were analyzed. High-resolution mapping was facilitated by using digital imaging microscopy and by analyzing extended (prometaphase) chromosomes. The map coordinates established by in situ hybridization showed a one to one correspondence with those determined by Southern (DNA) blot analysis of hybrid cell lines containing fragments of chromosome 11. Furthermore, by hybridizing three or more cosmids simultaneously, gene order on the chromosome could be established unequivocally. These results demonstrate the feasibility of rapidly producing high-resolution maps of human chromosomes by in situ hybridization.