Population Dynamics of Ditylenchus destructor on Peanut

The population development of Ditylenchus destructor in the roots, pegs, hulls, and seeds of eight peanut (Arachis hypogaea) genotypes was studied in the greenhouse. Although all genotypes tested were good hosts for D. destructor, differences in host suitability were observed. Invasion of the plant parts by Ditylenchus destructor proceeded more slowly in genotypes with long growth periods. During the second half of the growth period of these genotypes, D. destructor populations emigrated from the hulls and seeds into the soil but reinfected the pods after a few weeks. The genotypes with the longest growth periods supported the highest number of nematodes when each genotype was harvested at its usual harvest time. The long-season genotypes supported low numbers of nematodes when harvested before crop maturity.     

Pathogenicity of Criconemella curvata to Alfalfa

Large populations of Criconemella curvata and extended experimental periods were required to adversely affect yield of ''Moapa 69'' alfalfa. C. curvata ectoparasitic feeding caused a reduction in feeder root numbers and tap root size and small lesions on tap and secondary roots. Greater reproduction occurred at 27 C than at 22 C, but the effect of the nematode on alfalfa growth was the same at both temperatures.     

Pathogenic Potential of Tylenchorhynchus dubius on Selected Turfgrass

Tylenchorhynchus dubius was observed to feed on ''Toronto'' creeping bentgrass and ''Merion'' Kentucky bluegrass, and was a key participant in reducing the vegetative growth of both grass species. The severity of foliar and root macrosymptoms incited by T. dubius to ''Toronto'' bentgrass was greater on plants grown at 16 C than on plants maintained at 21, 27 and 32 C. These parasitized plants exhibited a suppression of secondary stolon formation, shortened internodes and premature inflorescence initiation. Initial inoculum densities of 500 and 1000 nematodes/test pot produced similar pathogenic effects on the host. Feeding was primarily on root hairs and epidermal cells immediately behind the meristematic region. No necrotic lesions or other diagnostic symptoms were visible at the feeding sites. Nematodes were not observed inside the roots.     

Pathogenicity of the Lesion Nematode,Pratylenchus brachyurus,on Six Soybean Cultivars

Pathogenicity tests of Pratylenchus brachyurus on selected greenhouse-grown soybean cultivars indicated the nematode reduced seed yield of ''Hood'' but not that of ''Custer'', ''Bragg'', ''Dyer'', or ''Pickett''. Root weights of all cultivars were reduced. Damage and numbers of nematodes within soybean roots growing at 13, 21, and 29 C were greater at higher temperatures. At 29 C, root pruning was prominent in ''Hood'' and ''Pickett'' but limited in ''Custer'' and ''Hill''. Root pruning was not observed at 13 C and only ''Pickett'' showed pruning at 21 C. Plant height and foliage weight were not affected. P. brachyurus had no effect on the emergence of ''Pickett'' or ''Bragg'' soybeans. Nematode counts from roots of ''Pickett'' at intervals after inoculation indicated that hatching of second generation second-stage larvae occurred about 15 days after egg laying. An average of 68% of the initial inoculum penetrated the roots within five days of inoculation, the highest observed was 81% in five days. Details of structural damage in penetrated tissues were studied in sectioned roots. In soybean roots infected by P. brachyurus and/or Rhizoctonia solani greater damage occurred with nematode and fungus combined than with either acting alone.     

Histological Studies of Ditylenchus africanus Within Peanut Pods

Ditylenchus africanus entered the immature pegs and pods of peanut (Arachis hypogaea cv. Sellie) at the peg-connection and subsequently invaded the parenchymatous regions of the hull exocarp and endocarp, and eventually the seed testa. The nematode caused malformations of the cells of infected tissues, cell wall breakage, and cell collapse. The damage appeared to be due to enzymatic activity. In some testae the entire parenchyma region, which aids in protection of the seed, was destroyed. In immature pods, the nematodes moved across the fibrous region of the mesocarp into the hull endocarp. In mature pods, however, the fibrous mesocarp of the hull was lignified and apparently was a barrier to penetration of the inner pod tissues. In late-harvested pods, increased numbers of eggs and anhydrobiotes were found in the hull tissues, and eggs in the seed testa, suggesting the onset of winter survival mechanisms of the nematode.     

Effect of high air and soil temperature on dry matter production,pod yield and yield components of groundnut

Groundnuts (Arachis hypogaea L.) grown in the semi-arid tropics are commonly exposed to air and soil temperatures above 35 °C during the reproductive period causing significant yield losses. The objectives of this study were to determine: (i) whether effects of high air and/or high soil temperature in two contrasting cultivars were similar; (ii) the effects of the timing of imposition of high air and soil temperature; (iii) the effects of high air, high soil and both stresses combined on yield and yield components; and (iv) whether the effects of high air and high soil temperature were additive or multiplicative. Plants were grown at optimum and ambient soil temperature from planting until start of podding at 45 d after planting (DAP) in Experiment 1, and until start of flowering at 28 DAP in Experiment 2. Thereafter, plants of each cultivar were exposed to a factorial combination of two air temperatures (optimum: 28°/22 °C and high: 38°/22 °C) and two soil temperatures (ambient: 26°/24 °C and high: 38°/30 °C) until final harvest at 90 DAP. The effects of high air and high soil temperatures imposed from start of flowering or podding were similar. Exposure to high air and/or high soil temperature significantly reduced total dry matter production, partitioning of dry matter to pods, and pod yields in both the cultivars. High air temperature had no significant effect on total flower production but significantly reduced the proportion of flowers setting pegs (fruit-set) and hence fruit numbers. In contrast, high soil temperature significantly reduced flower production, the proportion of pegs forming pods and 100 seed weight. The effects of high air and soil temperature were mostly additive and without interaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of the herbicide terbutryn on meiosis,yield and mitotic chromosomes in C2 plants ofVicia faba L.

The herbicide terbutryn induced up to 11.3 % chromosomal abnormalities in cells undergoing meiosis inVicia faba. The mean number of pods/plant and the mean number of seeds/pod were considerably reduced, but the average seed dry mass was not or was only slightly affected by this herbicide. In C₂ plants chromosomal abnormalities were observed in few but significant numbers of cells.     

Symptomatology and Histopathology of Soybean Roots Infected by Pratylenchus scribneri and P. alleni

Size of lesions caused by Pratylenchus scribneri on roots of ''Clark 63'' soybean was correlated with nematode colony size within roots. A single nematode was capable of causing a detectable lesion. When a root became highly necrotic and shrunken, few nematodes but numerous eggs remained in the tissue. In histological sections made 5, 11, 18, and 45 d after planting, P. scribneri was located entirely within the cortex and generally was oriented longitudinally to the vascular cylinder, either outstretched in the same plane or coiled through several cells. Nematodes moved intracellularly, causing extensive rupturing of cell walls, retraction and disappearance of cytoplasm, and thickening of cell walls and necrosis of cells around feeding sites. Depth of penetration within the cortex and necrosis of cells increased with time after infection, eventually resulting in formation of cavities in the cortex and occasional secondary injury to the endodermis. Stele tissue was unaffected by feeding, and damage to the epidermis was limited to nematode entry points. Orientation of P. alleni and histopathology of its infection at 45 days were identical to those of P. scribneri, except that there was no injury to the endodermis.     

Population Dynamics of Belonolaimus longicaudatus and Criconemella ornata and Growth Response of Bermudagrass and Overseeded Grasses on Golf Greens Following Treatment with Nematicides

Portions of a ''Tifgreen'' bermudagrass golf green with poor turf and large numbers of Belonolabnus longicaudatus and Criconemella ornata were treated with selected nematicides in the summers of 1977 and 1978. Improvements in turf quality were observed within 4 wk after treatment with phenamiphos and fensulfothion. Treatment with phenamiphos restulted in lower numbers of B. longicaudatus 4 and 14 wk after treatment in the 1977 experiment and up to 1 yr after treatment in the 1978 experiment. Treatment with fensulfothion reduced the number of B. longicaudatus for only 1 month after treatment and significantly increased the numbers of this nematode in September and March in the 1978 experiment, Negative correlations were obtained between numbers of B. longicaudatus and turf qualily up to 1 yr. Numbers of C. ornata were reduced only in January and June following treatment with phenamiphos and not at any time with fensulfothion. Treatment with fensulfothion resulted in higher numbers of this nematode than in check plots in November and March. The percent area covered by prostrate spurge the following year was reduced following treatment with phenamiphos, but not with fensulfothion.     

Soil pH Effects on Nematode Populations Associated with Soybeans

''Amsoy'' soybeans were grown for 2 months in nonsterilized Jackson silt loam amended to pH 4.0, 6.0, and 8.0. Nematodes were extracted biweekly from soil and roots. The greatest numbers of Pratylenchus alleni colonized soybean roots at pH 6.0. Hoplolaimus galeatus and members of the Tylenchinae-Psilenchinae survived best at pH 6.0, while numbers o f the Dorylaimoidea were greatest at both pH 6.0 and 8.0. The non-stylet nematodes were recovered in greater numbers from pH 8.0 soil. Potassium, manganese, and phenols were highest in soybean plants grown in pH 4.0 soil, the pH at which there were the fewest nematodes. A thicker suberized outer layer o f root tissue occurred in plants grown at pH 4.0.     

Penetration and Development of Meloidogyne arenaria on Two New Grape Rootstocks

Penetration, development, and reproduction of a virulent ''Harmony'' population of Meloidogyne arenaria was studied on two nematode-resistant grape rootstocks 10-17A and 6-19B. ''Cabernet Sauvignon'' was used as a susceptible control for comparison. Plants were inoculated with 100 freshly hatched second-stage juveniles (J2) of M. arenaria. Greater numbers of J2 penetrated roots of ''Cabernet'' than 10-17A, and none penetrated roots of 6-19B 4 days after inoculation (DAI). At 7 DAI, vermiform J2 advanced to sausage-shaped J2 in roots of ''Cabernet,'' penetrated roots of 6-19B, and had egressed from roots of 10-17A. Resistant rootstocks expressed hypersensitive responses to penetrating J2 along the root epidermis, among the cortical cells, and along the differentiating vascular bundles. At 13 DAI, 68% of the J2 had attained globose stage in roots of ''Cabernet,'' whereas there was no development of vermiform J2 in roots of the other two rootstocks. The nematodes reproduced only in roots of ''Cabernet.'' Lack of development of J2 in roots of the two resistant grape rootstocks might be the result of a hypersensitive response to J2 feeding.     

The Physiology of Groundnut

The distribution of labelled assimilates following the assimilation of ¹⁴CO₂ in groundnut (Arachis hypogaea L.) by single leaves at different nodes was investigated using autoradiographic technique. In the vegetative stage growing leaves assimilated most of the ¹⁴carbon, while the fully expanded leaves exported most of its radiocarbon to the apices, young expanding leaves and to the roots. Soon after the formation of the pegs and the growth and development of the pods, the developing pods become the major sinks. At this stage translocation from the foliage of each branch was restricted mostly to the pods produced by this branch.     

Conifer Stored Resources and Resistance to a Fungus Associated with the Spruce Bark Beetle Ips typographus

Bark beetles and associated fungi are among the greatest natural threats to conifers worldwide. Conifers have potent defenses, but resistance to beetles and fungal pathogens may be reduced if tree stored resources are consumed by fungi rather than used for tree defense. Here, we assessed the relationship between tree stored resources and resistance to Ceratocystis polonica, a phytopathogenic fungus vectored by the spruce bark beetle Ips typographus. We measured phloem and sapwood nitrogen, non-structural carbohydrates (NSC), and lipids before and after trees were attacked by I. typographus (vectoring C. polonica) or artificially inoculated with C. polonica alone. Tree resistance was assessed by measuring phloem lesions and the proportion of necrotic phloem around the tree''s circumference following attack or inoculation. While initial resource concentrations were unrelated to tree resistance to C. polonica, over time, phloem NSC and sapwood lipids declined in the trees inoculated with C. polonica. Greater resource declines correlated with less resistant trees (trees with larger lesions or more necrotic phloem), suggesting that resource depletion may be caused by fungal consumption rather than tree resistance. Ips typographus may then benefit indirectly from reduced tree defenses caused by fungal resource uptake. Our research on tree stored resources represents a novel way of understanding bark beetle-fungal-conifer interactions.     

Reproductive Variability of Field Populations of Meloidogyne spp. on Grape Rootstocks

Variability in penetration, development, and reproduction of two resistance-breaking field pathotypes (pt.) of Meloidogyne arenaria, M. incognita, and a population of mixed Meloidogyne spp. virulent to grape hosts were compared on two resistant Vitis rootstocks ''Freedom'' and ''Harmony'' in separate tests. ''Cabernet Sauvignon'' was included as a susceptible host to all four nematode populations. Secondstage juveniles (J2) of the mixed population failed to penetrate Freedom roots. By contrast, 6% of J2 in the M. incognita population penetrated Freedom roots but did not develop beyond the swollen J2 stage. The two resistance-breaking populations of M. arenaria differed in their virulence except on susceptible roots of Cabernet Sauvignon. More J2 of M. arenaria pt. Freedom penetrated Freedom roots and reached adult stage than did M. arenaria pt. Harmony. Later life stages of M. arenaria pt. Freedom occurred earlier and in greater numbers in Harmony roots than did M. arenaria pt. Harmony. Reproduction of M. arenaria pt. Freedom was greater in Freedom and Harmony roots than M. arenaria pt. Harmony. Thus, one population of M. arenaria is highly virulent and the other is moderately virulent.     

Structural Changes Associated with Resistance of Soybean to Heterodera glycines

Subcellular responses to infection by Race 3 of Heterodera glycines in susceptible (''Lee'') and resistant (''Forrest'' and ''Bedford'') soybean cultivars were compared. Syncytial formation, initiated in susceptible as well as resistant soybean cultivars, was characterized by wall perforations, dense cytoplasm, and increased endoplasmic reticulum, In susceptible plants, syncytia developed continuously until nematode maturity. This included hypertrophy of nuclei, increase of rough endoplasmic reticulum in early stages of infection, and formation of wall ingrowths at a late stage of infection. In the resistant reaction in Forrest, a necrotic layer surrounded syncytium component cells demarcating them from surrounding normal cells and leading to syncytial necrosis. Wall appositions were prominently formed near the necrotic layer, and the cytoplasm of the syncytium component cells was extremely condensed. The whole syncytium became necrotic at a late stage of infection. Bedford had nuclear degeneration prior to cytoplasmic degradation. Chromatin was often scattered throughout the syncytial cytoplasm. Finally the whole syncytium became degenerated with plasmalemma completely detached from the syncytial cell walls. The differences in resistant responses reflect a difference in genetic composition of the soybean cultivars tested.     

外源乙烯利施用时期对花生源库形成的调控效应

为了解决源库关系不协调而限制花生产量提高的问题,在大田栽培条件下,以‘山花9号’花生为试验材料,设置花后10、20、30 d 3个喷施时期,以不喷施处理为对照,探讨不同时期喷施乙烯利对花生源库形成的调控效应。结果表明: 花后10和20 d喷施乙烯利可显著减少花生的开花数量、果针数、幼果数,提高秕果数和饱果数,而花后30 d喷施处理对开花数量、果针数和幼果数无抑制作用。喷施乙烯利可以增加花生单株叶面积,开花后10 d喷施处理的单株叶面积增幅最大,随着喷施时期的推迟增幅减小。花后10和20 d喷施乙烯利显著提高了花生叶片的光合速率,但花后30 d喷施处理只能在短期内提高光合速率,对生育后期的叶片光合速率无显著影响。从源库综合性状来看,花后20 d喷施乙烯利的源库关系最协调,有利于促进同化物向荚果的运输,提高有效果比例和荚果充实度,从而提高产量。因此,喷施乙烯利是解决花生“花多不实、果多不饱”源库失衡现象的有效措施,生产中使用乙烯利控花应选择在开花后20 d喷施。     

Biocontrol Efficacy Among Strains of Pochonia chlamydosporia Obtained from a Root-Knot Nematode Suppressive Soil

Three Pochonia chlamydosporia var. chlamydosporia strains were isolated from a Meloidogyne incognita-suppressive soil, and then genetically characterized with multiple Pochonia-selective typing methods based on analysis of ß-tubulin, rRNA internal transcribed spacer (ITS), rRNA small subunit (SSU), and enterobacterial repetitive intergenic consensus (ERIC) PCR. All strains exhibited different patterns with the ERIC analysis. Strains 1 and 4 were similar with PCR analysis of ß-tubulin and ITS. The strains'' potential as biological control agents against root-knot nematodes were examined in greenhouse trials. All three P. chlamydosporia strains significantly reduced the numbers of nematode egg masses. When chlamydospores were used as inoculum, strain 4 reduced egg numbers on tomato roots by almost 50%, and showed effects on the numbers of J2 and on nematode-caused root-galling. A newly developed SSU-based PCR analysis differentiated strain 4 from the others, and could therefore potentially be used as a screening tool for identifying other effective biocontrol strains of P. chlamydosporia var. chlamydosporia.     

Transgenic apple plants overexpressing the Lc gene of maize show an altered growth habit and increased resistance to apple scab and fire blight

Transgenic apple plants (Malus × domestica cv. ‘Holsteiner Cox’) overexpressing the Leaf Colour (Lc) gene from maize (Zea mays) exhibit strongly increased production of anthocyanins and flavan-3-ols (catechins, proanthocyanidins). Greenhouse plants investigated in this study exhibit altered phenotypes with regard to growth habit and resistance traits. Lc-transgenic plants show reduced size, transversal gravitropism of lateral shoots, reduced trichome development, and frequently reduced shoot diameter and abnormal leaf development with fused leaves. Such phenotypes seem to be in accordance with a direct or an indirect effect on polar-auxin-transport in the transgenic plants. Furthermore, leaves often develop necrotic lesions resembling hypersensitive response lesions. In tests, higher resistance against fire blight (caused by the bacterium Erwinia amylovora) and against scab (caused by the fungus Venturia inaequalis) is observed. These phenotypes are discussed with respect to the underlying altered physiology of the Lc-transgenic plants. The results are expected to be considered in apple breeding strategies.