Forms and degrees of resistance in Populus spp. to the Melampsora leaf rusts occurring in Australasia
TL;DR: The Sub-section Albidae, the only major taxomonic grouping of Populus immune to both Melampsora larici-populina Kleb, and M. medusae Thum, leaf rusts in the field in Australasia, is worthy of fuller investigation for use in commercial and aesthetic plantings.
Abstract: Summary The Sub-section Albidae, the only major taxomonic grouping of Populus immune to both Melampsora larici-populina Kleb, and M. medusae Thum, leaf rusts in the field in Australasia, is worthy of fuller investigation for use in commercial and aesthetic plantings. Preliminary investigations indicate that race-specific resistance is common in the Aigeiros Section of Populus and this has significant implications in the establishment of clones of this Section. Rust resistance, disease progress pattern and length of growing season of clones are important considerations in the selection of clones for certain purposes in particular environments.
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TL;DR: Comparative measurements have shown that during the period 1974–1981 the growth rate of pines established among the eucalypts was approximately ten times greater than that of the native trees.
Abstract: Pinus radiata is spreading from plantations into some types of native eucalypt forest. A broad transect through one heavily invaded site was mapped in 1974 and re-examined after intervals of time. In 1977 the adjacent pine plantation was clear-felled for commercial purposes. By 1981 it was clear that the pines that had already invaded the eucalypt forest were contributing their own progeny to the mixed stand. However, the rate of recruitment is slow due to high seedling mortality. Comparative measurements have shown that during the period 1974–1981 the growth rate of pines established among the eucalypts was approximately ten times greater than that of the native trees.
37 citations
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TL;DR: Responses by quarantine and forestry authorities to the inadvertent introduction to Australia of seven economically important pests and pathogens of forest trees, or forest products, from the time of introduction to the present are described.
Abstract: Summary Responses by quarantine and forestry authorities to the inadvertent introduction to Australia of seven economically important pests and pathogens of forest trees, or forest products, from the time of introduction to the present are described. Eradication was achieved only in the case of European house borer (Hylotrupes bajulus). but not for West Indian drywood termite (Cryptotermes brevis), five-spined bark beetle (Ips grandicollis). Sirex wood wasp (Sirex noctilio), poplar rusts (Melampsora medusae and M. larici-populina) and Dothistroma needle blight (Dothistroma septospora). It has not been possible to quantify the economic cost of eradication attempts, or of control measures including research, for any of the case histories presented. It is argued that the Australian Agricultural Health and Quarantine Service should be actively involved in control campaigns until effective pest or disease management strategies have been developed.
29 citations
Journal Article•
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TL;DR: The strong additive genetic variation and potentially high heritability in resistance within current breeding populations of P. radiata augurs well for the successful incorporation of needle blight resistance into future breeds via traditional general-combining-ability seed orchards.
Abstract: Three separate studies showed that New Zealand populations of Pinus radiata D. Don possess useful quantitative genetic variation in resistance to infection by the fungus Dothistroma pini Hulbary. Heritability of resistance was high enough under suitable conditions to allow effective selection and breeding for resistance. In the first study, 66 "resistant" trees were phenotypically selected in heavily diseased New Zealand plantations in 1966; 21 of these subsequently retained a strong measure of resistance when clonally propagated by cuttings. However, only five clones were judged acceptable in growth, branching, and stem straightness. In the second study, clonal variation in resistance to natural infection by the fungus was sharply exhibited in hedged clonal archives from 2and 3-yearold second-generation ortets (originally selected for growth and stem quality, but not for resistance). Although closely related hedged clones sometimes differed considerably in their susceptibility to infection, there were still significant mean differences in the susceptibility of families, attributable almost entirely to general combining ability effects of the parents. Variation in susceptibility was also strong among hedges of clones aged 18-23 years. The third study showed dramatically that there were marked genetic differences among 5-year-old trees in resistance to infection under natural inoculation in the field. The study involved a diallel cross among 25 seed orchard clones. General combining ability effects were very strong, while specific combining ability effects were negligible. Individual full-sib families ranged from 3% to 69% in proportion of progeny badly infected. The strong additive genetic variation and potentially high heritability in resistance within current breeding populations of P. radiata, already improved in growth and stem quality by intensive selection and breeding, augurs well for the successful incorporation of needle blight resistance into future breeds via traditional general-combining-ability seed orchards. INTRODUCTION The needle blight disease caused by the fungus Dothistroma pini* (syn. Dothistroma septospora (Dorog.) Morelet) is the most serious threat yet to the health of New * Dothistroma pini is the imperfect stage of Scirrhia pini Funk & Parker. New Zealand Journal of Forestry Science 12(1): 14-35 (1982) Wilcox — Resistance to Dothistroma needle blight 15 Zealand's forests of P. radiata. It could also become important in Australia (Edwards & Walker 1978). Heavy infections can cause severe defoliation to young stands over large areas, thereby slowing down the growth of the trees. If left unchecked in areas of high disease hazard, infection can kill young trees, as has commonly occurred in Kenya (Allen 1973; Gibson 1972, 1979). Since 1966, outbreaks of the disease have been countered by aerial spraying with copper fungicide (Kershaw et al. 1979). Chemical spraying is fully accepted in New Zealand as a worthwhile immediate control measure against Dothistroma needle blight but it is not always effective in preventing re-infection and increment loss, and is becoming more expensive because of rising costs and the ever-increasing area of susceptible trees (60 000 ha sprayed in 1979 and 105 000 ha in 1980). The severity of needle blight attack fluctuates from year to year according to weather conditions; wet summers promote the heaviest attacks. The disease is now obviously permanent in New Zealand, but strains of resistant P. radiata are unlikely to evolve here by natural selection as long as spraying continues. Artificial selection and breeding for resistance offers an alternative or complement to spraying as a method of reducing the disease hazard, provided that exceptionally virulent mutant forms of D. pini doi not subsequently appear. Breeding for resistance in P. radiata could be accomplished in several ways: • Hybridisation with resistant, other closed-clone pines, such as Pmus patula Schiede & Deppe; • Selection of the most resistant provenances (Burdon & Bannister 1973; Cobb & Libby 1968); • Selection and crossing of resistant parent trees from local stands or breeding populations. In an investigation into the third of these possibilities, emphasis was given to establishing whether or not genetic variation in Dothistroma needle blight susceptibility within New Zealand P. radiata is great enough and sufficiently heritable to allow breeding of resistant strains. To be economically significant, resistance must effectively defend the crop against the disease. It could be sufficient to avoid having to spray at all, or at least so often. Alternatively, "effective" resistance combined with other silvicultural devices such as using cuttings instead of seedlings, early pruning, and heavy thinning, could help maximise the benefits from spraying in reducing inoculum load and minimising increment loss. PHENOTYPIC SELECTION FOR RESISTANCE There is obvious phenotypic tree-to-tree variation in Dothistroma needle blight resistance in any infected stand. A strong environmental component in this variability is often apparent, most noticeably in the localised severity of defoliation of trees growing in damp gullies, and other "hot spots" resulting from early spread from initial infection centres. "Within areas of heavy infection, however, it is possible to find individual trees that show "field" resistance; these are likely to be either chance escapes or genetically resistant trees. 16 New Zealand Journal of Forestry Science Vol. 12 No. 1 (1982) During October and November 1966, 79 apparently resistant trees were selected from 7to 15-year-old heavily diseased, genetically unimproved P. radiata stands at Kaingaroa and Tokoroa that had never been sprayed with copper fungicides (Forest Research Institute 1968). About 220 ha of uniformly heavily infected and defoliated stands were systematically searched for healthy green trees; no account was taken of stem form, branching characteristics or growth rate. The stands were mostly naturally regenerated second crops which had been thinned and some of them had been pruned. All were growing on volcanic ash soils. The trees that were still noticeably free of infection compared with their neighbours by May 1967 were retained as "resistant" plus-trees ("867" series*). These 66 selected "867" series clones were established in clonal tests of rooted cuttings at Rotorua and in Kaingaroa Forest in July 1968. The tests also included several clones not selected for needle blight resistance, from ortets aged 9-40 years, and some seedlings of a routine seedlot. Artificial inoculation using overhead frames covered with infected pine needles was employed in the Rotorua test, while natural infection was relied on in the two Kaingaroa tests, which were located inside heavily diseased stands in Compartments 44 and 913. After 18 months the cuttings were clearly more resistant than seedlings (Table 1). There were no very marked differences in resistance between cuttings from ortets of different ages (cf. Garcia & Kummerow 1970), or between clones selected for resistance and unselected clones. There were, however, statistically significant differences between clones within both the selected and unselected groups. TABLE 1—Mean defoliation 18 months after planting
28 citations
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TL;DR: Six mono-uredospore isolates (races) of Melampsora medusae Thiim produced qualitatively distinct reactions, in vitro, when incubated at 15 °C on leaf disks of certain cultivars of Populus deltoides Marsh, suggesting differential race-cultivar-temperature interaction in the epidemiology of M.medusae.
Abstract: Six mono-uredospore isolates (races) of Melampsora medusae Thiim. produced qualitatively distinct reactions, in vitro, when incubated at 15 °C on leaf disks of certain cultivars of Populus deltoides Marsh. The infection types in some race-cultivar combinations were very temperature sensitive with less distinct reactions when incubated at 20 or 25°C. The significance of differential race-cultivar-temperature interaction in the epidemiology of M. medusae is discussed.
11 citations
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TL;DR: Race, cultivar, light intensity of incubation and species of Cladosporium interacted significantly to determine disease level (uredinial number) on the leaf disks and the percentage of these uredinia subsequently colonized by the Cladospora spp.
Abstract: Antagonism of five species of Cladosporium to production of uredinia by three races of Melampsora larici-populina on leaf disks of poplar (Populas × euramericana) was generally higher with races A and E but lower with race D, at high light intensity (400 μ Em−2s−1) than at low light intensity (100 μ Em−2s−1). Colonization by all species of Cladosporium, of the uredinia induced by the races on the cultivars, was higher at the low than at the high light intensity. The extent of reduction in colonization with increasing light intensity depended on the race, cultivar and species of Cladosporium involved. While the species of Cladosporium was the most important major factor affecting both uredinial production and colonization, race, cultivar, light intensity of incubation and species of Cladosporium interacted significantly to determine disease level (uredinial number) on the leaf disks and the percentage of these uredinia subsequently colonized by the Cladosporium spp.
4 citations
References
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TL;DR: In a recent review, Nelson suggested that the term of horizontal resistance with quantitatively expressed resistance 'horizontal resistance' was unacceptable as currently defined and implied that it was the durability of resistance that was of primary redefine horizontal resistance as resistance "that reduces the concern to the breeder".
Abstract: In a recent review, Nelson (10) suggested that the term of horizontal resistance with quantitatively expressed resistance 'horizontal resistance' was unacceptable as currently defined. The that their results were interpreted by Dinoor (2) as indicating that definition referred to was that given by van der Plank (12) as there could be differential interactions, or race-specificity, in follows: \"When the resistance is spread against all races of the horizontal resistance. The most important feature of the resistance pathogen we shall call it horizontal or lateral\" and \"By definition, of Joss Cambier for the breeder was that, even though horizontal resistance is spread evenly against all races\". In other intermediate, it was quickly overcome (3). words, horizontal resistance was defined as not race-specific. To These results show that incomplete or intermediate resistance is Nelson these definitions were unacceptable because van der Plank not necessarily horizontal and that it is false to conclude that then described the potato cultivars Kennebec and Maritta as each resistance is horizontal because it is intermediate. It is only having intermediate horizontal resistance to some races of possible, therefore, to demonstrate that resistance is horizontal by Phytophthora infestans and complete 'vertical' (race-specific) testing it against many different cultures of a pathogen. Even if resistance to others. The resistance of these two cultivars therefore many cultures are used without revealing race-specificity, the use of was greater towards some races than others and Nelson suggested one more culture might demonstrate that resistance is not that this conflicted with the definition of horizontal resistance but horizontal. My colleagues at the Plant Breeding Institute and I satisfied van der Plank's definition of vertical resistance. Nelson agreed that absolute proof of horizontal resistance is impossible. implied that it was this confusion of ideas that led Johnson and Law There was no doubt, however, that resistance of some cultivars had (5) to describe the resistance of certain wheat cultivars to yellow lasted a long time in commercial use while that of others had not rust as 'durable' rather than horizontal. He then proposed to and that it was the durability of resistance that was of primary redefine horizontal resistance as resistance \"that reduces the concern to the breeder. Therefore, in 1972 I suggested to my apparent infection rate\" and supposed that Johnson and Law colleagues that resistance that lasts a long time should be called might have been happy to use the term horizontal resistance thus durable. These arguments were not explicity presented by Johnson defined. and Law (5) who indicated that resistance of certain wheat cultivars Unfortunately he is mistaken in this supposition. I believe that to yellow rust could not be called horizontal because they had one of the most misleading ideas connected with the concept of greater resistance to some races of P. striiformis than to others. horizontal resistance is the belief that it can be recognized as any This statement was criticized on one count by van der Plank (13). In resistance that reduces the apparent infection rate, in contrast to addition, I accept that, in theory, a cultivar could possess both vertical or race-specific resistance which, it has been suggested (12), vertical and horizontal resistance. Nelson (10) appears to have only delays the onset of an epidemic. Horizontal resistance was overlooked the distinction between the definition of types of equated by van der Plank with resistance that reduces the infection resistance and their manifestation in a single cultivar. Our rate, as illustrated by his statement \"the infection rate and therefore statement (5) would have been more accurate if we had indicated horizontal resistance are the main theme of this chapter\" (12, p. that we were unable to prove that the durable resistance we were 164). studying was horizontal, especially towards races of P. striiformis Browder (I) showed that the slow-rusting characteristic of not used in our experiments. Bulgaria 88 wheat to leaf rust (caused by Puccinia recondita) was The term durable was proposed because, it embodied fewer race-specific and could be overcome by certain strains of the assumptions than did the concept of horizontal resistance and it pathogen. He concluded that slow-rusting of the type seen in easily conveyed an important practical aspect of resistance to both Bulgaria 88 could slow down the rate of development of epidemics specialists and laymen. Durable resistance can only be recognized in a way similar to that attributed to horizontal resistance by van in cultivars that have been widely grown for a reasonably long der Plank, although, in showing race-specificity, it clearly was not period (3); such cultivars are therefore especially valuable in horizontal resistance. There are many examples of wheat cultivars studies of the factors leading to durability of resistance and in with intermediate levels of resistance to some races of P. striiformis, breeding for more durable resistance. I am aware that the able to slow down the development of epidemics of those races, but recognition of durable resistance is a retrospective judgment. It is with greater susceptibility to other races (8,9,11,14). Johnson and preferable to accept this as a fact rather than to presume that Taylor (7) agreed with Browder that slowing down an epidemic is resistance will be durable from the observation that it is not solely a characteristic of horizontal resistance. The wheat intermediate, or to make the unprovable claim that resistance is cultivar Joss Cambier was considered to have incomplete but horizontal. The fact that it can only be recognized retrospectively is adequate resistance to yellow rust when first released commercially no barrier to its use, once recognized, in breeding programs (3). in Britain in 1967. In 1971 high levels of yellow rust were observed Whether it is transferred successfully by breeding will, again, only on it and an isolate of P. striuformis from these infections was become clear after sufficient testing. It is worth remembering, compared with an earlier isolate that caused moderate infections on however, that this limitation applies to all systems of controlling Joss Cambier (6). A differential interaction between these isolates plant diseases over the long term, including the widespread use of and the wheat cultivars Hybrid 46 and Joss Cambier showed that fungicides, cultivar mixtures, or multilines. the resistance of Joss Cambier, although incomplete, was racespecific and therefore not horizontal. Johnson and Bowyer (4) LITERATURE CITED confirmed these results, yet so strong is the idea of the association
67 citations
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TL;DR: This proposes that at least two factors are involved, one attached to the pollen (P) and one to the stigma (S) and that the interaction of these (PS) is critically involved in the total process.
Abstract: Interspecific compatibility and incompatibility have been examined through the genus Populus. General methods of manipulation have been developed to break the incompatibility barriers. These methods are described and a hypothesis is put forward to account for the results. This proposes that at least two factors are involved, one attached to the pollen (P) and one to the stigma (S), and that the interaction of these (PS) is critically involved in the total process. Implications for future plant breeding are discussed.
50 citations
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TL;DR: Both M. medusae and laricipopulina have been recorded in Australia for the first time, and the possible effect of these rusts on Australian forestry is discussed, and several other rusts in Australia with known conifer aecial hosts elsewhere are listed.
Abstract: Melampsora medusae Thum. and M. larici-populina Kleb. have been recorded in Australia for the first time. Their detection, spread and host range are described. M. medusae has the wider host range, but occurs mainly on Populus deltoides clones and hybrids. M. laricipopulina occurs mainly on P. nigra var. italica. Detailed descriptions are given of both rusts, and their geographic distribution listed. The possible effect of these rusts on Australian forestry is discussed, and several other rusts in Australia with known conifer aecial hosts elsewhere are listed.
40 citations
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TL;DR: Four mono-uredospore isolates of Melampsora larici-populina produced qualitatively distinct reactions on four half-sib clones of Populus deltoidesMarsh and thus were recognisable as races.
Abstract: Four mono-uredospore isolates of Melampsora larici-populina
Kleb. produced qualitatively distinct reactions on four half-sib clones of Populus deltoides
Marsh. and thus were recognisable as races. Two of the races could be distinguished equally readily by the distinctness of their reactions (three quantitative parameters) on four compatible clones of Populus spp. The pronounced race specific reactions of the clones of P. deltoides, allied to the less distinct, but nevertheless race specific reactions, of the compatible clones are consistent with an integrated rather than a disjunctive concept of resistance in Populus spp. to M. larici-populina.
20 citations
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TL;DR: Clones of Populus spp.
Abstract: SUMMARY Clones of Populus spp. growing in a relatively uniform field environment near Canberra appear to differ in the form and degree of resistance to the two leaf rusts Melampsora medusae Thum, and M. larici-populina Kleb. There is evidence of considerable racial specialisation in both rust species and this has importance in future breeding strategies for poplar. Although both rust species occurred at low and high latitudes in eastern Australia in 1975, in midsummer M. medusae was most common on clones at low latitudes while M. larici-populina was most frequent on the same clones at higher latitudes. Fungal hyperparasites of both rusts are common in the field in autumn. A programme for further research on poplar rusts is outlined.
18 citations
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