Mature Plant Resistance Research Articles

Natural resistance to bean yellow mosaic potyvirus in subterranean clover

Seed of 31 named cultivars and 11 other genotypes of Trifolium subterraneum (subterranean clover) was sown in 3 major and 3 smaller scale field experiments. In these, bean yellow mosaic virus (BYMV) was spread from infector plants to test rows by naturally occurring aphids. The numbers of clover plants developing BYMV symptoms in each row were counted at different times. Based on the results from at least 2 field experiments, different genotypes were assigned to 1 of 5 BYMV infection categories (A-E), ranging from greatest (A) to least (E) infection. Category A was found to contain genotypes that were latest maturing while, except for cv. Rosedale (ssp. brachycalycinum) which was in E despite being of intermediate maturity, category E contained earliest maturing genotypes. Except for cv. Rosedale, when the percentages of plants with BYMV symptoms in the 3 main experiments were plotted against days to flowering previously established for each genotype, the two were closely related. However, when young plants of cultivars in categories D or E were aphid-inoculated with 2 BYMV isolates, they became infected to a similar extent to young plants of 2 late-maturing cultivars from category A. This suggests that, except for cv. Rosedale, the extent of BYMV infection obtained in the field was determined by plant physiological age, plants of late-maturing genotypes being easier for viruliferous aphids to infect with BYMV than plants of early-maturing genotypes of the same age but physiologically older, a phenomenon known as 'mature plant resistance'. When plants of cv. Rosedale were aphid-inoculated with 7 different isolates of BYMV, a systemic hypersensitive reaction developed with 5 isolates but not with two others. This suggests that cv. Rosedale has 'strain specific hypersensitive resistance' to BYMV. No systemic hypersensitive reaction developed when the same 7 BYMV isolates were aphid-inoculated to cv. Dwalganup and named selections Pink Flowered and Northam Early, genotypes previously reported to react hypersensitively to potyvirus infection. The field screening procedure employed is suitable for use by T. subterraneum breeding programs seeking to develop new cultivars with resistance to BYMV. Cultivar Rosedale may prove a suitable source of resistance to use as a parent in crossing programs aimed at producing cultivars with natural BYMV resistance.

Mature plant and tissue resistance in the groundnut-peanut bud necrosis virus system

Leaves and plants of different ages of a susceptible and two resistant groundnut genotypes were mechanically inoculated with peanut bud necrosis virus, and the percentage of plants with systemic symptoms (incidence) and the incubation period were determined. The incidence decreased sharply in all three genotypes with the age of the inoculated leaves and plants. The incubation period increased with the age of leaves and plants. Apparently, only young tissue of young plants is susceptible, while mature tissue and plants are highly resistant. This mature tissue and plant resistance occurs irrespective of the susceptibility level of the genotype to peanut bud necrosis virus, however, it develops earlier in the resistant than in the susceptible genotypes.

Plant Age and Isolate Source Affect Expression of Downy Mildew Resistance in Broccoli

Resistance to downy mildew [Peronospora parasitica (pers.) ex. Fr.] in broccoli (Brassica oleracea L. Italica Group) depends on plant age. Seedling resistance seems to be independent of mature-plant resistance, where a mature plant is defined as having eight or more leaves. Our results suggest that, by using mature-plant resistance, an almost continuous variation instable levels of mature-plant resistance can be developed. Similarities in the response of mature plants of various lines to isolates from California, Washington, New York, and South Carolina indicated that the predominant race was the same at all locations. Correlations between resistant and susceptible responses to isolates from California, Washington, New York, and South Carolina varied from r = 0.48 to 0.74 depending on isolate source. The results indicated that selecting for high levels of resistance in mature plants at one location should result in good resistance elsewhere in the United States. Selecting immature plants (three to six leaves) may provide less reliable results due to the transitional status of the plant; i.e., between seedling and mature plant.

The development of mature plant resistance in four potato cultivars against aphid-inoculated potato virus YO and YN in four potato cultivars

Field-grown potato plants of cvs King Edward, Record, Maris Piper and Desiree were inoculated on seven different dates during the growing season of 1987 and 1988 with either potato virus YO (PVYO) or PVYN, using three viruliferous peach-potato aphids (Myzus persicae) per plant. In each cultivar, the proportion of progeny tubers infected with PVYO or PVYN was high in plants inoculated during the four weeks following emergence, the proportion declining to zero or close to zero in the subsequent 4–6 wks.

Mature plant resistance of barley to barley leaf rust, another type of resistance

Seedling and flag leaves of three barley cultivars were simultaneously inoculated with urediospores of barley leaf rust, race 1-2-1, and incubated at the same greenhouse bench. The inoculated leaves were harvested before urediospore formation was initiated. The volume of a large number of colonies was estimated by measuring colony area and colony depth by embedding the colony containing leaf segments into paraffin for microtome cutting. The colony volume was considerably smaller in flag leaves than in seedling leaves even in the extremely susceptible cultivar. On average the difference was about tenfold.

Importance and control of potato virus YN (PVYN) in seed potato production

The tobacco veinal necrosis strain of potato virus Y (PVYN) first became epidemic in several European countries in the 1950s. To prevent PVYN-infections, account must be taken of virus sources both within and without potato fields; for forecasting, the aphid vector species, their vector efficiency, and their flight activity must all be known. Well-timed haulm destruction needs knowledges of PVYN-translocation in potato plants and of the development of mature plant resistance. For successful virus control, also reliable methods for virus detection are needed, and for this ELISA has been well established for many years in seed potato certification schemes. A combined treatment of mineral oil and pyrethroids reduces aphid populations and the spread of stylet-borne viruses in the fields. In breeding for resistance, the major gene Ry induces complete protection against infections of all known PVY-strains.

Aphid migration and the importance of some aphid species as vectors of potato virus Yo (PVYo) in Sweden

The relationship between the occurrence of alate aphids and the proportion of progeny tubers infected by potato virus Yo (PVYo) was studied in 7 regions of Sweden from 1976 until 1984. The importance of mature-plant resistance and the proportion of PVYo diseased potato source plants were also considered.

Comparison of Seedling and Mature Plant Resistance to Phytophthora parasitica in Tomato

Abstract Seedlings of 11 genotypes of tomato (Lycopersicon esculentum, Mill.) were inoculated at the first true leaf stage with zoospores of Phytophthora parasitica under controlled conditions and evaluated for resistance based on seedling death. The same lines also were transplanted into two fields naturally infested with P. parasitica and grown to maturity. Disease severity in the field was evaluated based on plant death and canopy collapse prior to harvest. Resistance to P. parasitica was present in both commercial lines and accessions of L. esculentum var. cerasiforme (Dun.) A. Gray. Seedling resistance was generally a good predictor of resistance in mature plants. The relative resistance and susceptibility expressed in seedlings was reflected in 10 of 11 genotypes in the field. One cultivar that was susceptible in the seedling test appeared resistant in the field. Expression of resistance in both the seedling test and field was influenced by environmental factors.

Development of barley leaf rust, Puccinia hordei, infections in barley. I. Effect of partial resistance and plant stage

The fate of Puccinia hordei, race 1-2-1, infection units in seedlings and adult plants was followed from the moment appressoria were formed over the stomata. This was done in six spring barley cultivars, ranging from absolutely no partial resistance against barley leaf rust (‘L94’) to good partial resistance (‘Vada’). Infection units can abort anywhere between appressorium formation and sporulation. The abortions were classified into three groups: The cultivars differed significantly for Ap in the adult plant phase, not in the seedling phase. For EA cultivars varied significantly in both plant phases. With LA the cultivar effects were more pronounced in the adult plant phase. In seedlings the proportions AP, EA and LA among cultivars ranged from 0.03 to 0.05, from 0.04 to 0.39 and from 0.04 to 0.11 respectively. In the adult plants the respective ranges were from 0.04 to 0.20, from 0.07 to 0.26 and from 0.06 to 0.26. The size of the mycelial colonies measured at the same moment (7 to 8 days, depending on the series, after inoculation) varied widely between cultivars, especially in the adult plants. In de adult plant phase the linear correlation coefficients between partial resistance and the four histological parameters Ap, EA, colony size measured at the same moment, and LA were 0.95, 0.62, 0.80 and 0.16 respectively. Seedlings appeared considerably less representative than adult plants for a study of the relation between partial resistance and the histological parameters of fungal growth in the host tissue. It is concluded that the host pathogen interaction evens occurring during stoma penetration and very shortly after that are of decisive importance in the expression of partial resistance; it has the characteristics of a recognition process. The colony size in adult plants remains far behind those in seedlings suggesting another type of resistance, provisionally named mature plant resistance, besides partial and hypersensitive resistance.

Mature-plant resistance of potato plants against potato virus YO (PVYO)

Mature-plant resistance of potato plants against potato virus YO (PVYO) was studied in field experiments in 1976–1979 in southern Sweden. At intervals of 7 days, from mid June until mid August, PVYO was mechanically inoculated to one well-developed upper leaf per stem of each plant. Each week, a new group of plants were inoculated. In 1976–1977, the natural spread of PVYO by aphids was studied in relation to three different stages of potato plant development. The results of mechanical inoculation demonstrated that mature-plant resistance increases during July in southern Sweden but there were great differences between developmental stages. Early planting with sprouted seed resulted in plants with a considerable mature-plant resistance in mid July when late developed potato plants still were very susceptible.

Inheritance of Mature Plant Resistance to Helminthosporium maydis Race 0 in Maize1

Inheritance of resistance of inbred NC250 of maize (Zea mays L.) to southern corn leaf blight incited by Helminthosporium maydis Nisik. & Miy. race 0 was investigated using seedlings and mature plants. Reactions of seedlings artificially inoculated in greenhouse tests indicated resistance was recessive and ratings of three parents were B73 susceptible, B73rhm resistant, and NC250 segregating. Mature plant ratings by contrast were B73 and B73rhm susceptible and NC250 resistant. Most mature plant evaluations were made under severe natural epiphytotics in south Florida where 25 to 50% of the foliage of susceptible cultivars was usually destroyed by flowering time. Parents, F1, F2, F3, and backcross generations were rated on a scale of 1 (resistant) to 5 (susceptible) in increments of 1.0 or 0.5. Generation mean and diallel analyses indicated mainly additive effects for reaction to H. maydis race 0. Resistance conditioned by rhm‐gene was generally satisfactory to about flowering and then declined in effectiveness; however, rhm‐gene influenced mature plant resistance as demonstrated by comparisons between 200 F3 families in each of two populations: F3's from B73rhm ✕ NC250 and B73 ✕ NC250 averaged 2.2 and 3.3 for leaf blight ratings and 48.5 and 10.0 for the percentage of families in the three most resistant classes, respectively. These comparisons demonstrated enhancement of mature plant resistance by a gene for resistance in the seedling stage. Segregation ratios for F2 plants and F3 families indicated two recessive complementary loci for resistance while quantitative analyses estimates suggested this interpretation was an over simplification. The mature plant resistance of NC250, which persisted through the reproductive stage to near physiological maturity, was largely independent of reaction in the seedling stage, was not complex, and maybe transferred by backcrossing.

Colonization and sporulation of Peronospora viciae on cultivars of Pisum sativum

The behaviour of Peronospora viciae was examined on four pea (Pisum sativum) cultivars (Maro, Superb, Victory Freezer and Surprise) which appeared to exhibit varying degrees of resistance to this pathogen. Penetration into all cultivars was similar and mainly by direct entry through the cuticle. The pathogen grew in a similar manner and at a similar rate in all the cultivars during the early stages (<96 h) of tissue colonization. As it approached the onset of sporulation its growth slowed down in the more resistant cultivars but in no instance were any hypersensitive or other host cell reactions observed. Greater differences between the cultivars were seen in the extent of sporulation, with the least resistant cultivar (Superb) bearing the largest number of sporangiospores. There was much less sporulation on the most resistant cultivar (Maro) and the process was more dependent on temperature than it was on Superb. The development of mature plant resistance occurred in a similar way and on a similar time‐scale in all cultivars. The youngest leaflets on plants which were less than 8 weeks old at inoculation showed the least resistance to infection and colonization.

Changes in leaf components and peroxidase activity of potato plants (cv. Bintje) in relation to mature-plant resistance to PVYN

It can be of economic importance for seed potato growers to know the stage of mature-plant resistance of a crop to viruses when aphid flights occur. In 1976 four field experiments were carried out in different parts of the northern Netherlands in which potato plants were artificially inoculated with potato virus YN at four dates. Leaves, tubers and total crop growth were analysed during the growing season to see if a biochemical test could be used to determine the onset of mature-plant resistance. It is concluded that such a test is useful only when used in combination with additional information about early infections. None of the criteria (dry matter, organic nitrogen, chlorophyll and soluble protein contents, and peroxidase activity) proved to be useful in establishing or predicting the time of occurrence of a high level of mature-plant resistance with the desired accuracy.

Mature plant resistance of potato against some virus diseases. III. Mature plant resistance against potato virus YN, indicated by decrease in ribosome-content in ageing potato plants under field conditions

The concurrence of a decrease of the concentration of ribosomes and glycoproteins in leaves of potato plants under field conditions and mature plant resistance against potato virus YN was studied. On four of five dates with intervals of one or two weeks plants of randomly chosen plots in the field were inoculated. During plant growth sixth, tenth and fifteenth leaves of main stems were collected at regular intervals. With the aid of cellulose columns and polyethylene glycol-containing solvents the ribosome- en glycoprotein-contents (and in one experiment also the RNA-content) of these leaves were determined. Tubers were harvested from plants, inoculated fourteen days before. Lack of typical virus symptoms on plants grown from these tubers gave information on the presence of mature plant resistance. It was concluded that in plants which had developed about 20 leaves, there was a high degree of mature plant resistance when ribosome- and glycoprotein-contents in the fifteenth leaf was less than 2 and 4 OD260/ml/g fresh weight respectively. When higher absorbance values are measured, mature plant resistance may or may not occur depending on environmental conditions. The ribosome- and glycoprotein-contents have a remote relation to the mature plant resistance. It is suggested that ribosome- and glycoprotein-contents of the youngest fully expanded leaves give the best indication of mature plant resistance. In veldproeven werde het verband tussen de concentraties van ribosomen en glycoproteinen in bladeren van aardappelplanten en de ouderdomsresistentie tegen aardappel YN-virus (PVYN) bestudeerd. Op vier of vijf data met tussenpozen van een of twee weken werden planten in het veld met PVYN geinoculeerd. Gedurende de groeiperiode van de planten werden zesde, tiende en vijftiende bladeren op vastgestelde tijden verzameld. Chromatografische analyse met behulp van cellulosekolommen en solvents die polyethyleenglycol bevatten, leidde tot de bepalingen van de ribosoom- en glycoproteinegehalten (en in een proef ook het RNA-gehalte) in de verzamelde bladeren. De oogst van de knollen vond plaats 14 dagen na inoculatie. Het niet tot ontwikkeling komen van de typische virussymptomen bij planten, die uit deze knollen waren gegroeid, was een aanwijzing voor het optreden van de ouderdomsresistentie. Geconcludeerd wordt dat waarschijnlijk enige mate van ouderdomsresistentie tegen PVYN in een pootaardappelgewas aanwezig is, als het ribosoom- en glycoproteinegehalte in het vijftiende blad van hoofdstengels met ongeveer twintig bladeren, leidt tot corresponderende extinctiewaarden bij 260 nm per ml en per gram vers gewicht van respectievelijk minder dan 2 en 4. Wanneer hogere extinctiewaarden worden gevonden kan ouderdomsresistentie wel of niet in belangrijke mate voorkomen, afhankelijk van de omstandigheden waaronder het gewas is gegroeid. Gesuggereerd wordt de jongste volledig ontwikkelde bladeren te gebruiken voor het aantonen van een gelijktijdig optreden van de afname in de ribosoom- en glycoproteinegehalten en een praktisch waarneembare mate van ouderdomsresistentie.

Western gall rust, a serious disease ofPinus radiatain California

Summary Western gall rust, caused by Peridermium harknessii J. P. Moore, causes severe disease on nearly all species of hard pines including Pinus radiata, and presents a potential threat to the softwood industry of Australia and New Zealand should the pathogen be accidentally introduced into these countries. The pathogen causes formation of stem galls, which kill young trees and result in stem defect in older trees. In several regions of Australia where P. radiata is the main softwood species, it is likely that environmental conditions may be suitable for outbreaks of disease epidemics. There is some evidence that variation in resistance to western gall rust occurs both within and between native populations of P. radiata. In the event of introduction of P. harknessii into Australia the future of radiata pine may depend on the utilisation of genetically controlled resistance, mature plant resistance and suitable management practices.

Mature plant resistance of potato against some virus diseases. III. Mature plant resistance against potato virus YN, indicated by decrease in ribosome-content in ageing potato plants under field conditions

Mature plant resistance of potato against some virus diseases. III. Mature plant resistance against potato virus YN, indicated by decrease in ribosome-content in ageing potato plants under field conditions

Mature plant resistance of potato against some virus diseases. I. Concurrence of development of mature plant resistance against potato virus X, and decrease of ribosome and RNA content

Four of five weeks after planting a group of potato plants ‘Bintje’ was inoculated with potato virus X (PVX). Other groups were inoculated at intervals of 14 days. Tubers produced by plants inoculated 35 days after planting were all infected. The plants inoculated 49 days or later after planting produced few infected tubers. The latter had developed mature plant resistance against PVX infection. The ribosome and RNA contents of leaves were measured by application of adsorption chromatography. A rapid decrease in ribosome and RNA contents occurred in plants at the time of rapid increase in the rate of mature plant resistance. The decrease was most distinct in the fifteenth leaf and therefore the contents in this leaf seem to give a good indication of the rapid increase in resistance.

Mature plant resistance of potato against some virus diseases. II. Mature plant resistance and the influence of temperature on the ribosome and RNA content in leaves

Potato plants ‘Bintje’ were grown in growth chambers; one group of 27 plants at a daily regime of 15 h light and 9 h darkness with corresponding temperatures of 18 °C and 12°C, and a second group of 27 potato plants at a daily regime of 15 h light and 9 h darkness with corresponding temperatures of 22 °C and 17 °C. The plants of both groups were inoculated with potato virus X (PVX) 56 days after planting. Young leaves had a 3-fold higher ribosome and RNA content than ageing leaves. The decrease occurred earlier at 22 °C than at 18 °C.

Peronospora manshurica on a nonhost and on resistant, susceptible, and intermediate soybeans

Soybeans with mature plant resistance and a nonhost, string bean, were inoculated with Peronospora manshurica. Soybeans resistant, susceptible, and intermediate in reaction were inoculated for comparison. Leaves were fixed, cleared, and stained, and whole mounts were made daily. Individual infection sites were examined, and hyphae were measured microscopically. Spore germination varied as a result of self-inhibitory factors. Where it occurred, entrance by the fungus appeared identical on each plant at 12 h. Hyphal growth became rapid in susceptible tissue 36 h after inoculation; growth slowed, starting at 72 h in mature tissue, and was uniformly slow in tissue intermediate in resistance. Hyphal growth after 36 h was essentially zero in resistant tissue, but paradoxically it was sometimes rapid on nonhost tissue. Haustoria occurred in all plants inoculated. The number of haustoria per lesion increased in proportion to the length of hyphae, except on resistant tissue, where the number of haustoria per millimetre of hyphae was very low.

Translocation of the potato viruses YN and YO in some potato varieties

In experiments on the rate of translocation of the potato viruses YN and YO in the varieties Bintje, Eigenheimer, Dore and Sirtema it was found that both viruses infect tubers of Bintje much more readily than those of Eigenheimer. The tubers of the four varieties proved to be infected by PVYN to a higher degree than by PVYO. Tubers of the variety Dore became infected by PVYN to a very high degree, whereas the PVYN infection of those of the variety Sirtema reached the same level as Bintje tubers. Mature plant resistance could be demonstrated with respect to both viruses, but it was much more pronounced in the experiments with PVYO than in those with PVYN.