The application of habitat templets and traits to hyphomycete fungi in a mid-European river system

1. The general knowledge about hyphomycetes is summarized and traits of some of these organisms in the Rhône floodplain are described to assess compliance with the river habitat templet (RHT) and patch dynamics concept (PDC) hypotheses. This investigation corresponds with those for other taxonomic groups reported in a recent Freshwater Biology Special Issue on the Ecology of the Upper Rhône River (Statzner, Resh & Dolédec, 1994). 2. Three groups of fungi were considered: aquatic, terrestrial, and aero-aquatic hyphomycetes. 3. The main factors controlling distribution of these micro-organisms are food (mostly organic matter), dissolved oxygen and biotic interactions. 4. With contrasting strategies, hyphomycetes exploit both fallen leaves, a discrete ephemeral resource, and wood fragments, which are more durable. 5. Fungal propagules (spores, hyphae) are distributed in the water, and even the air, largely throughout the year. This explains the resilience of these organisms to disturbance. 6. A major problem is the spatial (boundary layer, dead zones) and temporal (leaf input) scale at which these micro-organisms live and their interactions at the scale adopted for the other organisms referred to in the Special Issue on the Ecology of the Upper Rhône. 7. Our scant knowledge of the microbial ecology in the Rhône floodplain, together with the scale problem and high microbial resilience to environmental stress, render the RHT and PDC hypotheses difficult to test. Only three traits could be tested on hyphomycetes, but all three confirmed the RHT hypotheses. 8. Hyphomycete communities appear to be biologically controlled in more favourable and temporally stable environments, and physico-chemically controlled in harsher and more perturbed environments.     

Lipid Metabolism in Dehydrating Peanut Kernels

Metabolism of radioactive lipids in kernels from peant plants subjected to ¹⁴C₂ under field conditions was studied during dehydration (curing) of the seeds at 22°C or 50°C. Synthesis of lipid was predominant during the first 6 to 12 hours of dehydration whereas degradation dominated between 12 to 24 hours of curing. These changes were related to the moisture content of the dehydrating kernels; a moisture range of 42 to 47% was found to be an important factor influencing the observed pattern of lipid metabolism. The results from the present study also indicate compartmentalization of lipid metabolism in dehydrating peanut kernels.     

Embryo Rescue in Wide Crosses in Arachis. 2. Embryo Development in Cultured Peg Tips of Arachis hypogaea

Embryo rescue techniques in Arachis are potentially importantfor recovering interspecific hybrids which have the propensityto abort. Pegs are commonly produced in interspecific crosses,but either they fail to reach the soil because growth is arrested,or pods are produced but embryo development is never re-initiated.Peg tips, with the ovule and embryo, of A. hypogaea L. cv. ‘NC6’, were used to determine whether peg tips can be usedas nurse tissue for in vitro culture of embryos. Tissues werecollected 1, 2, 3 and 4 d after self-pollination, after whichpeg meristems were removed from half the pegs, and culturedon five media combinations. Continued reproductive developmentwas observed for embryos cultured at all four collection days;however, the highest frequency of growth was observed in 1-d-oldtissues. Evidence is presented that meristematic activity mayrestrict embryo growth in the 2- to 4-d-old embryos and, oncethe sequence of events is initiated to slow embryo growth, itis not easily reversed in vitro. Achievements of embryo growthto multicellular, globular stages (stages 1–1 or 1–2)encourage the development of methods to recover very young embryosthrough tissue-culture techniques. Embryo culture, morphology, interspecific hybridization, Arachis hypogaea, comparative light and scanning electron microscopy, peanuts, groundnuts     

Embryo Rescue in Wide Crosses in Arachis. 1. Culture of Ovules in Peg Tips of Arachis hypogaea

Interspecific hybridization in Arachis is restricted by earlyembryo abortion for many cross-combinations. Rescue of youngembryos in vitro within a week after fertilization is necessaryto recover these embryos before they abort. Peg tips, with theovule and embryo tissues, of A. hypogaea L. cv. ‘NC 6’,were cultured to compare ovule growth, callus production andpeg elongation. Tissues were collected 1, 2, 3 and 4 d afterself-pollination, after which peg meristems were removed fromhalf the pegs and cultured on five media combinations. One-day-oldpegs had significantly (P = 0.01) more ovule growth than oldertissues. Presence of the meristem had a greater inhibition toovule growth for 2- to 4-d pegs than for 1-d-old pegs. Significantlymore callus was produced on 4-d pegs than younger tissues, andkinetin had the greatest stimulatory effect on callus. Elongationof pegs with the meristem attached was observed most often inmedia with high sucrose levels. The observations indicate thatvery young ovules can be grown in vitro, and techniques maybe applicable to rescue of young embryonic tissues of Arachis. Ovule culture, interspecific hybridization, Arachis hypogaea, peanuts     

ADJUSTING ROASTED PEANUT ATTRIBUTE SCORES FOR FRUITY ATTRIBUTE AND NONOPTIMUM CIELAB L* VALUES1

Developing peanut breeding strategies for roasted peanut flavor improvement requires that roasting be to an optimum and effects of negative environmental exposure be to a minimum. In practice it is difficult to achieve these conditions. However, statistical adjustments are possible. To ascertain the proper adjustments, surface response equations were determined relating roast color and fruity attribute scores to roasted peanut attribute score. Fruity attribute had a depressing effect on roasted peanut attribute score. Similarly, underroasting as well as overroasting led to reduced roasted peanut attribute scores. Adjusting for genotype and location had nonsignificant effects on mean optimal roast color or linear equation slope values of the fruity-roasted peanut relationship. With these findings a method for maximization of roasted peanut values was developed using a modified SAS routine. Although the capability to estimate the roasted peanut flavor of a sample with optimal roasting and environmental effects has several potential applications, our specific application is to evaluate parentage contribution to flavor enhancement or flavor reduction.     

Comparative Embryo Sac Morphology at Anthesis of Cultivated and Wild Species of Arachis

Introgression of germplasm from wild to cultivated species ofArachis is severely impeded because abortion processes oftenoccur as a prepeg-, peg-(gynophore), or postpeg-elongation event.A comparative study of embryo sac morphology at anthesis wasundertaken to determine if observable differences were presentthat could possibly explain abortion prior to peg tip swellingfollowing soil penetration. Two wild Arachis species (A. duranensisand A. stenosperma) plus A. hypogaea cultivars NC 6 and Argentinewere studied. Differences in starch grain concentration andcytoplasmic stranding organization were observed between A.hypogaea cultivars and the wild Arachis species. These differencesprobably have a significant impact on energy availability atsyngamy and the subsequent early cell division of the embryo.An improper energy balance could contribute to the onset ofabortion in interspecific hybrids. Modification in egg apparatusorganization among all species was also observed which may accountfor low percentages of seed recovery resulting from interspecifichybridization attempts. Embryo sac morphology, interspecific hybridization, Arachis hypogaea L., Arachis species, light microscopy, scanning electron microscopy, embryo abortion, fertilization incompatibility, peanuts, groundnut     

An experimental study of the breakdown of submerged leaves by hyphomycetes and invertebrates in Morocco

SUMMARY. 1. Mechanisms of the breakdown of submerged leaves under the warm and dry Moroccan climate, including the interaction between hyphomycetes and invertebrates, were investigated.
2. Laboratory experiments were performed on dried leaves of Salix sp. and Nerium oleander .
3. During the first month under the experimental conditions, Melanopsis praemorsa, Physa acula (Gastropoda) and Hydropsyche maroccana (Trichoptera), respectively, were responsible for a loss of weight of 38, 21 and 13% in willow leaves, and 40, 15 and 8% in oleander leaves.
4. The weight lost by willow leaves inoculated with the fungi Alatospora acuminata, Anguillospora longissima, Lemonniera aquatica and Tetracladium marchalianum increased with time, but varied according to the fungal species. Loss of weight and increase in nitrate and phosphate content of the leaves were greatest with Lemonniera and smallest with Tetracladium .
5. When the leaves thus colonized by each of the four fungal species were exposed to each of the three invertebrates, the amount of material consumed increased with the time of fungal conditioning and varied according to the fungus and to the invertebrate. Greatest consumption was by Melanopsis feeding on leaves conditioned by Lemonniera , in which case assimilation percentage by the gastropod was as high as 75%.
6. Owing to their numbers in the field, and to the quantity of leaf material they ingest, gastropods appear as the main shredders in the streams considered, thus replacing the Crustacea that often play this part under temperate climates. Breakdown seems faster in Morocco than in France, mainly because of a shorter initial time lag in weight loss.