Virulence Genes in Heterodera glycines: Allele Frequencies and Ror Gene Groups Among Field Isolates and Inbred Lines

ABSTRACT Genetic variation in field populations of Heterodera glycines is a key issue for both resistance gene deployment and basic understanding of virulence-gene flow in populations. In this study, we examined phenotypically defined genes for virulence under selection from host resistance. We separated the most common H. glycines genotypes in the United States into two virulence groups, based on their reproductive abilities on the resistant soybean plant introduction (PI) 88788. These groups correspond to previously identified virulence genes in the nematode, as follows: the dominant gene in H. glycines to PI88788, and the recessive genes to PI90763 and Pickett/Peking. Virulence allele frequencies and virulence genotype frequencies of selected field isolates were investigated by testing the host range of single-female-derived lines, which were developed through single-female inoculation on the standard susceptible soybean 'Lee 68'. By comparing virulence genotype frequencies between the original field isolates and their single-female-derived lines, we were able to determine allele frequencies in the field populations. The results suggest that tremendous variation in H. glycines virulence genes exists among field populations. Potential mechanisms of selection which could cause virulence genotype frequency increases are discussed as related to population genetics equilibrium theory.     

Veld management recommendations ‐ a reassessment of key species and proper use factors

One of the main reasons for the poor acceptance of traditional veld management systems by South African farmers is the inflexibility of these systems. Present recommendations indicate that both research and extension personnel appreciate the advantages of the recently‐developed multicamp approach. Within this framework special attention should now be paid to policy relating to selective grazing, key species and proper use factors. Local studies on nutritive value and the relationship between height of defoliation and percentage utilization, emphasize the importance of the choice of key species. A generalized use factor of 50% removal in the growing season is proposed as an interim guide for grassveld management. The need for simplification of recommendations is emphasized.     

Ranking of grass species according to visible wilting order and rate of recovery in the central orange free state

Abstract

A number of grasses were ranked according to the order in which they wilted with diminishing moisture availability, and according to their ability to recover after water replenishment. Digitaria eriantha and Digitaria argyrograpta were the most sensitive to moisture stress, whereas Sporobolus fimbriatus and Panicum stapfianum were last to show signs of wilting. The latter two grass species were the first to recover from wilting during optimum soil water conditions. The leaf water potential and soil water content at which each grass species wilted were recorded.     

Evaluation of the grazing potential of grass species in Tarchonanthus veld of the northern cape 1

Abstract

The grazing value of the seven most prominent grass species in Tarchonanthus‐limeveld was investigated from 1977 to 1981.

The frequency of utilization of Chrysopogon serrulatus was exceptionally high (93%), while Sporobolus fimbriatus, Themeda triandra and Digitaria seriata were intermediate (50–60%) followed by Cymbopogon plurinodis (34%). Eragrotis lehmanniana and Fingerhuthia africana were poorly grazed (12 to 16%). The utilization of species was influenced by stocking rate. Statistical differences between species indicated a relatively high biomass production (600 to 740 g DM/m² per year) for E. lehmanniana, C. plurinodis and T. triandra, while F. africana, S. fimbriatus and D. seriata were intermediate (320 to 420 g DM/m² per year). E. lehmanniana, C. plurinodis and T. triandra produced the highest above‐ground phytomass, but had a lower crude protein content (2,9 to 7,4%) and digestibility (46,1 to 61,3%) than the other four species (3,8 to 9,7% crude protein and 50,5 to 68,4% digestibility).     

Grond‐ en afloopverlies bepalings vanaf natuurlike veld,met behulp van ‘n reënvalnabootser

Uittreksel

‘n Oorhoofse roterende reënvalnabootser is gebruik om die sediment‐ en afloopverliese vanaf natuurlike veld in verskillende suksessiestadia en teen verskillende hellings te bepaal.

Soveel as 94,34% van die toegediende hoeveelheid water en 5,74 t/ha sediment het verlore gegaan vanaf ‘n pionierbedekte veld met ‘n 2,42% helling. Die basale bedekking het van al die veranderlikes betrokke, die grootste bydrae tot afloopverliese gelewer, terwyl die helling ‘n nie‐betekenisvolle rol gespeel het. Beide basale bedekking en helling het ‘n betekenisvolle (P < 0,05) invloed op die hoeveelheid sedimentverliese, vanaf natuurlike veld gehad.

‘n Hoogsbetekenisvolle verwantskap tussen basale bedekking met sediment‐ (r² = 0,68) en afloopverliese (r² = 0,69) is verkry, terwyl die helling geen betekenisvolle verwantskap met sediment‐ en afloopverliese getoon het nie.     

Toepassíng van ‘n gronderosievergelyking op natuurlike veld van die sentrale oranje‐vrystaat

Uittreksel

‘n Oorhoofse roterende rcënvalnabootscr is gebruik orn numericse waardes vir sekere faktore van die universele gronderosi‐evcrgelyking vas te stel. Alhocwei dit tydens hierdie Studie nodig was om sekere belangrike aannames te maak, het die afgeleide data betekenisvol ooreengestem met die reënvalnabootserrcsultate. Dit het veral betrckking op gronderodeerbaarheid en die bedekking en bestuursfaktor.

‘n Voorbeeld vir die gebruik van die universele gronderosievergelyking vir die beraming van grondverliese onder natuurlike veldtoestande, word uiteengesit. Die berekende grondverlies vanaf ‘n pioniergrasbedekking (2% basale bedekking) op ‘n Huttongrondvorm en ‘n 4% helling in die Sentrale Oranje‐Vrystaat, bedra tot 3,86 t/ha/jaar teenoor slegs 0,61 t/ha/jaar vanaf ‘n klimaksbedekking (6% basale bedekking) op dieselfdc helling en grondvorm. Die berekende grondverliese vanaf ‘n Hutton‐ en Valsriviergrondvorm het nie betekenisvol van mekaar verskil nie.     

Root-knot nematode--directed expression of a plant root--specific gene

Root-knot nematodes are obligate plant parasites that induce development of an elaborate feeding site during root infection. Feeding-site formation results from a complex interaction between the pathogen and the host plant in which the nematode alters patterns of plant gene expression within the cells destined to become the feeding site. Expression of TobRB7, a gene expressed only in tobacco roots, is induced during feeding site development. The cis-acting sequences that mediate induction by the nematode are separate from those that control normal root-specific expression. Reporter transgenes driven by the nematode-responsive promoter sequences exhibit expression exclusively in the developing feeding site.     

‘N vergelyking tussen digitaria eriantha steud. subsp. eriantha (smutsvingergras) en eragrostis curvula (schrad.) nees (oulandsgras) as hooigewasse vir skape 1

Uittreksel

Smutsvingergras‐ en oulandsgrashooi is by drie bemestingspeile, naamlik 30 kg N + 2,8 kg P ha^‐1; 90 kg N + 8,3 kg P ha^‐1 en 150 kg N + 13,8 kg P ha^‐1 geproduseer. Die hooi is in alle voorgenoemde gevalle op twee verskillende stadia gesny, naamlik gedurende die pypstadium en gedurende die vroeë volwasse stadium (sodra bloeiwyses oopgegaan het).

Die hooi wat in alle voorgenoemde behandelings gesny is, is aan groepe skape op ‘n kafeteriastelsel gevoer om voorkeurinname te bepaal. Soortgelyke hooi is ook aan individuele skape gevoer om inname te bepaal.

Die resultate het aangedui dat skape deurgaans ‘n voorkeur aan Smutsvingergrashooi, bo oulandsgrashooi gegee het. Die verband tussen bemesting, snystadium en inname kon nie duidelik uit die resultate bepaal word nie. ‘n Verband tussen hoër in‐vitro verteerbaarheid en hoër fosforinhoud met inname kon uit die resultate afgelei word.

Die gebruik van oulandsgras as hooigewas is ‘n algemene praktyk, maar Smutsvingergras kan ook op grond van bevindinge in hierdie ondersoek as hooigewas vir skape aanbeveel word.     

Influence of soil pH and fertilization on the dry matter production,chemical composition and digestibility of perennial grasses: I. Anthephora pubescens nees 1

Abstract

The influence of soil pH and fertilization (N, P and Zn) on the dry matter (DM) production, chemical composition (crude protein, P, K, Ca, Mg and Zn content) and organic matter (OM) digestibility of Anthephora pubescens Nees was evaluated in pots. The highest Dm production was obtained in the neutral soil medium (pH 6,5 in H₂O). Both the acid (pH 4,5 in H₂O) and alkaline (pH 7,5 in H₂O) soil mediums adversely affected DM yield, crude protein (CP), Zn content and OM digestibility of A. pubescens. Fertilization invariably increased DM production.