Future Cultivars Research Articles

Lupin takes up less potassium but uses the potassium more effectively toproduce shoots than canola and wheat

We compared the potassium (K) response of canola (Brassica napus L. cv. Karoo), spring wheat (Triticum aestivum L. cv. Camm), narrow-leaf lupin (8 cultivars of Lupinus angustifolius L.), and yellow lupin (2 cultivars of L. luteus L.) in a glasshouse experiment. The following measures were used: yield without added K; K required for 75% of the maximum yield; K required to achieve a K concentration in shoots of 20 g/kg; K required to achieve a K content of 50 mg K/pot in dried shoots (K concentration multiplied by yield); and, for the L. angustifolius cultivars, the K efficiency ratio (yield for the nil-K treatment divided by yield for the largest amount of K applied).Both L. angustifolius and L. luteus used soil K and applied K more effectively than canola and wheat to produce shoots (measured from dried shoots of 42-day old seedlings). For all amounts of K applied, including the nil treatment, the K concentrations were higher in canola and wheat shoots than in shoots of the 2 lupin species. Consequently, the 2 lupin species were less effective than canola and wheat at taking up soil and applied K, but were more effective at using the K taken up to produce shoots. The most recent cultivar of L. angustifolius, cv. Kalya, was less effective than the older Merrit cultivar at using soil and applied K to produce shoots, therefore future cultivars need to be screened for their ability to use soil and applied K. The K efficiency ratio for L. angustifolius indicated cultivars Kalya and 2141 were inefficient and the following cultivars had similar medium efficiency values: Myallie, Tanjil, Tallerack, Quilinock, Belara and Merrit. As measured in 42 day old seedlings, the diagnostic critical concentration of K in shoots required for 90% maximum yield of dried shoots was about (g K/kg) 40 for wheat, 37�for canola, 16 for L. angustifolius and 14 for L. luteus.

Cost‐benefits of reduced aphicide usage on dwarf hops susceptible and partially resistant to damson‐hop aphid

SummarySoil‐applied imidacloprid at full (125 g a.i. ha−1) and half approved doses gave levels of control of damson‐hop aphid, (Phorodon humuli), similar to that provided by foliar spray(s) of tebufenpyrad on the aphid‐susceptible dwarf hop cvs First Gold and Herald. On those cultivars, aphid control was unreliable on plots treated with quarter dose imidacloprid and was generally no better than on untreated plants. Aphids were virtually eliminated from the leaves by the end of July each year in all treatments consistent with the action of natural enemies. Aphid contamination of cones reflected the numbers on foliage at flowering time, but varied widely between years. Yields and percentage α‐acids content of dried hops were unaffected by the numbers of aphids on leaves early in the season and in cones at harvest, but aphid contamination reduced the economic values of crops by as much as 80%. Few P. humuli colonised the partially aphid‐resistant breeding line 23/90/08 before their numbers were regulated and consistent with natural enemy activity. Yields, percentage α‐acids content, and commercial value of harvested cones were similar in all treatments on 23/90/08 whether or not plants were treated with aphicides. The commercial risks posed by P. humuli preclude substantial reductions in aphicide usage on aphid‐susceptible dwarf hop cultivars, but future cultivars expressing a similar level of partial resistance to aphids as 23/90/08 should not need treatment with aphicides.

Biplot Analysis of Test Sites and Trait Relations of Soybean in Ontario

Superior crop cultivars must be identified through multi-environment trials (MET) and on the basis of multiple traits. The objectives of this paper were to describe two types of biplots, the GGE biplot and the GT biplot, which graphically display genotype by environment data and genotype by trait data, respectively, and hence facilitate cultivar evaluation on the basis of MET data and multiple traits. Genotype main effect plus genotype by environment interaction effect (GGE) biplot analysis of the soybean [Glycine max (L.) Merr.] yield data for the 2800 crop heat unit area of Ontario for MET in the period 1994-1999 revealed yearly crossover genotype by site interactions. The eastern Ontario site Winchester showed a different genotype response pattern from the three southwestern Ontario sites in four of the six years. The interactions were not large enough to divide the area into different mega-environments as when analyzed over years, a single cultivar yielded the best in all four sites. The southwestern site, St. Pauls, was found to always group together with at least one of the other three sites; it did not provide unique information on genotype performance. Therefore, in future cultivar evaluations, Winchester should always be used but St. Pauls can be dismissed. Applying GT biplot to the 1994-1999 multiple trait data illustrated that GT biplots graphically displayed the interrelationships among seed yield, oil content, protein content, plant height, and days to maturity, among other traits, and facilitated visual cultivar comparisons and selection. It was found that selection for seed yield alone was not only the simplest, but also the most effective strategy in the early stages of soybean breeding.

Biplot Analysis of Test Sites and Trait Relations of Soybean in Ontario

Superior crop cultivars must be identified through multi-environment trials (MET) and on the basis of multiple traits. The objectives of this paper were to describe two types of biplots, the GGE biplot and the GT biplot, which graphically display genotype by environment data and genotype by trait data, respectively, and hence facilitate cultivar evaluation on the basis of MET data and multiple traits. Genotype main effect plus genotype by environment interaction effect (GGE) biplot analysis of the soybean [Glycine max (L.) Merr.] yield data for the 2800 crop heat unit area of Ontario for MET in the period 1994–1999 revealed yearly crossover genotype by site interactions. The eastern Ontario site Winchester showed a different genotype response pattern from the three southwestern Ontario sites in four of the six years. The interactions were not large enough to divide the area into different mega-environments as when analyzed over years, a single cultivar yielded the best in all four sites. The southwestern site, St. Pauls, was found to always group together with at least one of the other three sites; it did not provide unique information on genotype performance. Therefore, in future cultivar evaluations, Winchester should always be used but St. Pauls can be dismissed. Applying GT biplot to the 1994–1999 multiple trait data illustrated that GT biplots graphically displayed the interrelationships among seed yield, oil content, protein content, plant height, and days to maturity, among other traits, and facilitated visual cultivar comparisons and selection. It was found that selection for seed yield alone was not only the simplest, but also the most effective strategy in the early stages of soybean breeding.

Analysis of Resource Allocation in Final Stage Sugarcane Clonal Selection

Superior genotypes of sugarcane (interspecific hybrids of Saccharum spp.) must continue to be developed with current resources as selection criteria evolve and expand. Developing future cultivars of sugarcane for the Everglades Agricultural Area (EAA) of South Florida with high water table tolerance and increased P‐uptake efficiency could be an integral part of Everglades restoration. The objective of this study was to assess the current allocation of resources in the final selection phase of cultivar (clonal) development of the Canal Point, FL, sugarcane breeding program. Variance component analyses were conducted on elite genotypes from 7 yr of trials. Variance components were used to compare relative magnitudes of sources of variation and to explore more efficient use of resources. Variation attributable to crop × location interaction was nearly always the largest relative source of variation next to the residual term. The contributions to variance due to genotype × crop and genotype × location interactions were low, though these interactions cannot be discounted in cultivar release decisions. Variance due to replications was extremely low. Four statistics were used as metrics of experimental precision when reducing the number of replications. Reducing replications from eight to four did not compromise experimental precision. Removing the second‐year planting sequence compromised little, if any, useful information for effective cultivar release decisions. Better allocation of resources could be achieved by alternative experimental design scenarios. Testing for high water table tolerance or P‐uptake efficiency could also be included, improving ecological compatibility of agriculture in the EAA.

Shoot organogenesis from petiole explants in the aquatic plant Nymphoides indica

A protocol for rapid shoot organogenesis from petiole explants of the ornamental aquatic plantNymphoides indica L. Thwaites O. Kuntze was developed for use in future mutation breeding and cultivar selection studies. Optimum culture conditions for shoot organogenesis were determined. Effects of factorial combinations of 2-iP, BA or kinetin (0–25 μM) in factorial combination with IAA or NAA (0–25 μM) were examined. On the basis of regeneration frequency (80%) and adventitious shoot number (11.5 shoots per explant), most efficient shoot organogenesis occurred on petiole explants cultured on a basal medium consisting of full-strength MS inorganic salts, 0.56 mM myo-inositol, 1.2 μM thiamine-HCl, 116.8 mM sucrose supplemented with 10 μM BA and 20 μM IAA and solidified with 0.8% TC agar. Formation of adventitious shoots by direct and indirect shoot organogenesis from the same explant was verified by histological sectioning. With the exception of variegated leaf production on a single adventitious shoot produced in the presence of 25 μM kinetin and 15 μM NAA, no visible phenotypic abnormalities were observedin vitro in any of the shoots generated. Solid achlorophyllous adventitious shoots were recovered following culture of this variegated leaf tissue. Plantlets were easily acclimatized toex vitro conditions.

Suitability of new subterranean clovers in the Canterbury region

The annual legume, subterranean clover, is adapted to permanent pastures in the summer drought-prone areas of eastern New Zealand. Dry summers over the last decade in Canterbury have renewed the interest from farmers in the use of sub clover. As the previously used cultivars Mt Barker and Tallarook are no longer available, a trial was established at AgResearch Templeton to evaluate a new series of cultivars and breeding lines from Australia together with recent New Zealand selections. The lines were sown in rows in May 1993 and assessed for seed set, autumn seedling regeneration and spring growth under sheep grazing for 4 years. The new Australian cultivars had improved seed set and consistently better seedling regeneration and herbage yield compared with older cultivars. The late-flowering, small-leaved and densely branched types were best adapted to the Canterbury environment. The late-maturity cultivars Denmark and Leura, selected from Sardinian germplasm, re-established 50% more seedlings and produced 25% greater late winter/ spring growth than Mt Barker and Tallarook in the third year. The New Zealand selection Ak 948 had similar performance to Denmark and Leura but the remaining selections were mediocre by the fourth year. The Sardinian ecotype breeding material appeared well-adapted to Canterbury conditions and future cultivars based on this material may be most suitable. Further trials are required in harsher sites to confirm these cultivar recommendations. Keywords: Australian cultivars, dry regions, herbage yield, seedling regeneration, subterranean clover, Trifolium subterraneum

Approaches for breaching yield stagnation in wheat

This paper outlines the breeding objectives, methodology, and genetic gains of the international wheat breeding program of the International Maize and Wheat Improvement Center (CIMMYT) based in Mexico. The historical analysis of yield gains asserts that wise use of genetic diversity has been paramount in raising the yield ceiling and expanding genetic variability. Data is provided to support a philosophical view that yield potential per se should be combined with both abiotic and biotic tolerances in the breeding of future cultivars. The erosion of high yield potential should be avoided at all costs through a protective shield of wide-spectrum disease resistance genes.Key words: yield potential, shuttle breeding, Aegilops squarrosa.

Yield, Flowering, and Leaf Area Index of Okra‐Leaf and Normal‐Leaf Cotton Isolines

Cotton (Gossypium hirsutum L.) with alternative leaf morphologies, such as the cleft‐shaped okra‐leaf types, offers production advantages such as earlier maturity. However, okra‐leaf types have not been commercially viable in the USA. The objectives of this study were to test okra‐leaf types in genetic backgrounds varying in maturity and region of adaptation and to provide growth data that might explain yield differences. Four to seven pairs of selected cotton okra‐ and normal‐leaf isolines (and check cultivars) were grown in the field in one 2‐yr (Exp. A) and two 1‐yr experiments (Exp. B and C) from 1994 to 1996 near Stoneville, MS, in row spacings of 76 and 102 cm. In Exp. A, average lint yields of okra‐leaf isolines were greater overall than normal‐leaf lines (847 vs. 749 kg ha−1), but in Exp. C, the opposite was true (1020 kg ha−1 for okra‐ vs. 1130 kg ha−1 for normal‐leaf types). No yield difference was found between leaf types in Exp. B. Yields of okra‐leaf lines were either equal to or less than those of recently released high‐yielding commercial types whose okra‐leaf isolines are not yet available. Okra‐leaf types were usually 1 to 4 d earlier in maturity than their normal‐leaf counterparts, possibly contributing to their overall yield advantage in Exp. A. When only okra‐leaf isolines were considered, Tamcot HQ95 ranked first or second highest for yield and was the earliest to mature in all three tests. In general, the row‐spacing effect and interactions with row spacing were not significant. The results indicate that the okra‐leaf trait should be considered for producing future cultivars.

BREEDING AS A TOOL FOR IMPROVING POSTHARVEST QUALITY CHARACTERS OF LILY AND TULIP FLOWERS

Segregation of postharvest quality characters was studied in lily and tulip. A large variation in longevity of both lily and tulip flowers was found within populations tested at individual plant level. Other postharvest quality characters like number of flowers per stem, male sterility (lily) and stem elongation (tulip) also varied within the populations tested. Due to the high correlations between the offspring and their corresponding parental genotypes for several characters, breeding for a considerable improvement of postharvest quality in future cultivars seems promising.

Seed Yield and Residue Production of Lentil Cultivars Grown at Different Slope Positions

The presence of crop residue on the soil surface is important in controlling soil erosion, but residue amounts from lentil (Lens culinaris Medik.) are often insufficient to control soil erosion during subsequent phases of the cereal-grain legume cropping systems of the U.S. Pacific Northwest. To gain knowledge of residue production by lentil in typical production environments, six lentil cultivars were grown at four slope positions in southeastern Washington over 3 yr. Residue and seed production varied significantly among cultivars and slope positions (P < 0.01). Total residue production ranged from four to 20 times the 290 lb/acre required by conservation standards, however, the amount remaining after sowing of the subsequent winter wheat (Triticum aestivum L.) crop was much less, indicating that large losses occurred during harvesting and tillage operations. On lower slope positions, grain and residue yields were inversely correlated for all cultivars. On upper slope positions, grain yields were nearly constant among cultivars, but ‘Laird’ produced an average of 42% more residue than ‘Brewer’. No single cultivar met yield and residue production criteria across all landscape positions. Growers can improve erosion control by site-specific sowing of high-residue cultivars such as Laird. Breeding programs should consider the differences in the upper and lower slope positions for seed and residue production when selecting for cultivars with improved biomass production. Research Question Surface residue is a very important factor in preventing erosion on the steep slopes in the Palouse region of the Pacific Northwest. Lentils produce relatively small amounts of residue compared with wheat and other small grains and, in order to maintain sustainable farming systems in the region, this study was undertaken to identify lentil cultivars that produce large amounts of residue across a wide range of slope positions. Literature Summary The soils on the rolling hills of the Palouse region of eastern Washington, northern Idaho, and northeastern Oregon are becoming increasingly eroded. Soils on these slopes vary considerably in type and productivity. In general, the upper slope positions are less productive than the lower slope positions due to poorer soil types caused by erosion, leaching of nutrients, and reduced moisture content. Ironically it is the upper slope positions that are in greatest need of residue, however they are the positions that have the lowest potentia1 for residue production. In order to meet regulations regarding minimum surface residue levels set up by the Natural Resource Conservation Service, many fmers have incorporated tillage practices that leave a rough soil surface over the winter while others are eliminating lentil from their rotations altogether. Eliminating lentil from the current rotations could be quite detrimental to the small grain crops, since lentil crops return N to the soil and break up disease cycles. In order to make it more equitable for the farmer, lentil cultivars that produce high levels of residue in the poorer, upper slope positions must be identified. Study Description This study involved growing six lentil cultivars at the four main slope positions (topslope, backslope, footslope, and toeslope) determining their production potential at each. The experiment was conducted at three different locations over 3 yr (1984, 1985, and 1986). Samples of the mature crop were harvested from a 4 ft segment of the middle two rows in each plot. Total biomass, seed, and residue yields were recorded for each cultivar and harvest index was calculated by dividing seed yield by total biomass yield. Applied Questions How can lentil residues be increased to a sufficient level on the upper slope positions to significantly reduce erosion? This may be accomplished through site specific farming. Farmers would grow high residue producing cultivar on the upper slope positions while growing a cultivar that produced less residue on the lower positions. One caution with thi approach is that the two cultivars have to mature at nearly the same time. Often the crop on the upper positions will mature earlier than those on the lower posi tions due to lower moisture reserves. Can future cultivars be developed to produce adequate levels of residue? Lentil breeding programs should consider using residue production as a selection criteria when developing new cultivars. Recommendation Growers may consider site specific farming where a cultivar producing large amounts of residue are planted on the upper slope positions while a cultivar producing less residue could be planted on the lower slope positions where smaller amounts are needed.

ROSE BREEDING: PAST, PRESENT, PROSPECTS.

In this review the PAST, PRESENT and PROSPECT will be considered as three separate periods in the history of the breeding and development of rose cultivars. The recurring theme is the genetic variation. This theme was chosen because there is justified doubt as to sufficient genetic variation available among current progenitors to ascertain the vitality and productivity of future cultivars in cross-breeding. This seems particularly true for glasshouse cultivars. The above three periods are defined as follows. PAST: the era from pre-history until about the year 1875, the PRESENT era from about 1875 until 1967, and the PROSPECT (future) from 1967 onwards. With probably over 5000 years, the PAST covers the longest time lapse. It ended around the year 1875, with the discovery of aimed cross-breeding. Not accidentally, Mendel published his famous laws about inheritance about simultaneously. It is remarkable that many rose breeders still like to think in terms of Mendelian or qualitative inheritance. Quantitative inheritance or additive gene action, seems either little known or not used. The PRESENT period started with the knowledge about aimed cross-breeding, and ended with the introduction of biotechnology in rose breeding in 1967. This period has covered about 90 years only. The PROSPECT, which in fact is the FUTURE era, has already begun in 1967, and is about 28 years on the way. To start with, the breeding and genetic variation occurring in the PAST period will be considered. It is assumed that early horticulturists sampled desirable rose species from the wild and planted them in collections. According to Wiley (1955) and Krussmann (1987), several species and most likely cultivars of them too, were grown in gardens in China, Persia, Mesopotamia, Egypt, Greece and in Italy, long before the beginning of the Christian era. It is uncertain, however, whether all the roses of ancient horticulture were seedlings, or that certain strains were already vegetatively propagated. A fact is, that during this whole period, new cultivars exclusively arose by sowing the seeds that resulted from open-pollination. Particularly in the beginning, domestication of species and their probable inter-specific hybrids supposedly was a slow process. However, as unsuitable primitive forms were discarded and propagation methods improved, progress towards tame forms was more rapid. Introduction of new genotypes and exchange of species and cultivars by travellers, considerably broadened the genetic variation available to horticulturists. It should be noted, by the way, that domestication of a species, any species in fact, necessarily involves a narrowing of the genetic variation available. In a few cases only, early breeders kept record of the female parent and the year of introduction of a new cultivar. These records, however, have enabled to ascertain part of the descent of later cultivars Although it was instinctively felt that neighbouring plants in collections had a relation to the new forms obtained, breeders did not yet realize that characters of the male parent could be turned over by pollination. Afterwards, it was established that from initially mainly diploid, gradually new cultivars were and later tetraploids. Particularly nowadays, important cultivars are almost exclusively tetraploid. Modern research demonstrated that in crossing diploid and

Clone × Environment Interactions for Yellow-flesh Intensity in Tetraploid Potatoes

For the yellow-flesh fresh market, potato (Solanum tuberosum L.) cultivars with intense yellow-flesh are desired. The effects of clone, environment and clone × environment interactions on the intensity of the yellow-flesh trait in tetraploid potatoes were investigated. Twenty-four yellow-flesh clones, including 23 USDA selections and the check cultivar Yukon Gold, were evaluated for tuber yellow-flesh color as measured by a reflectance colorimeter in replicated field trials in Presque Isle, Maine in 1991 and 1992, and in Riverhead, N.Y., and Bridgeton, N.J., in 1992 and 1993. There were significant differences among environments and among clones for yellow-flesh intensity. The clone × environment interaction was also significant. Broad-sense heritability of yellow-flesh intensity was estimated as 0.93 with a 95% confidence interval of 0.92-0.97. The instabilities noted in some of these clones, although statistically significant, are of limited practical concern. The intensity of yellow-flesh will be an important trait for breeders to select in developing new yellow-flesh cultivars. However, in testing yellow-flesh clones for future cultivar release, the role of environment and clone environment interactions on other agronomic traits will probably be more important than the environment and clone environment interactions on the intensity of yellow-flesh.

Evaluation of Genotypes of Tall Fescue for Resistance to Puccinia-Graminis Subsp Graminis in Controlled Conditions

Eight commercial cultivars and one advanced breeding line of tall fescue (Festuca amndinacea) were screened for resistance to stem rust (Puccinia graminis subsp. graminis) in controlled conditions. Cultivar Melik and a breeding line (Melik Selection) showed high levels of resistance, while the other seven cultivars were highly susceptible. The results with cultivar Melik indicate the potential for resistance to be maintained or incorporated into future tall fescue cultivars. Within cultivars AU-Triumph, Demeter, Mozark, Pema and Southern Cross, individual plants showed moderate resistance to stem rust and this could be used as a source of resistance in a selection program.

Phalaris improvement in Australia

Abstract The genetic improvement of Phalaris aquatica L. and its scientific basis are reviewed. The few accessions made in the 1890s gave rise to cv. Australian. Trumble selected ‘Gb81’ within ‘Australian’. Major collections in 1951 and 1954 gave cultivars Sirocco and El Golea through selection within Moroccan ecotypes, and cultivars Sirosa, Sirolan, and Holdfast by hybridisation with ‘Australian’, followed by recurrent selection for various traits. Selection within the seed‐retaining Argentinian cultivar El Gaucho, gave ‘Seedmaster’, and a single mutant seed‐retaining plant within ‘Australian’ gave ‘Uneta’. Future cultivars are previewed and alternative selection methods, such as widespread testing of synthetics, are discussed.

DNA SEQUENCE POLYMORPHISM BASED GENETIC DIVERSITY STUDIES IN SWEETPOTATO GERMPLASM

Highly polymorphic DNA markers were identified in sweetpotato (Ipomoea batatas) using PCR amplification and arbitrary primers. More than 100 accessions representing US cultivars and their progenitors, and germplasm lines from around the world were analyzed. Sweetpotato germplasm exhibited high genetic variability and individual-specific profiles were obtained for all accessions. US cultivars formed a tight cluster in the principal coordinate analysis suggesting a narrow genetic base. The genetic relationship data of US cultivars and their progenitors based on DNA polymorphisms was in agreement with their known pedigree. The putative paternal parents of certain cultivars selected through open pollination were identified based on shared polymorphisms. The PCR-based markers are valuable in the characterization of sweetpotato germplasm and in ensuring a broad genetic base for future cultivars.

Evolutionary trends in morphological, physiological, agronomical and qualitative traits of Triticum aestivum L. cultivars bred in Italy since 1900

The agronomical, physiological and qualitative characteristics of 34 representative cultivars of bread wheat belonging to 7 generations (groups) of cultivars produced by Italian breeders over 90 years have been evaluated.Cultivars were grown for three years in replicated trials with two husbandry conditions : old, simulating that in use in the first part of the century, and modern.It was found that there was a reduction of plant height, an increase in harvest index, reduction of the vegetative growth phase associated with a progressive increase of yield potential. With the old husbandry the cultivars did not show a clear positive trend in yield potential, indicating that genetic improvement was largely dependent on or associated with a parallel improvement of growing conditions.The greatest genetic gain was achieved with the last generation of cultivars which, with modern husbandry, produced 830 kg ha−1 more than those of the previous group. This is an indication that breeding is not approaching a yield plateau and emphasizes its major role in accelerating the increase in yield potential. Moreover, modern cultivars have better quality indices than those of the previous groups, suggesting that Italian breeders were able to manipulate the genes controlling protein composition while selecting genotypes characterized by a shorter straw and an higher yield potential.It is concluded that in the present economic and political context where farmers are forced to optimize and probably to reduce inputs, old cultivars may be used in breeding programmes for low input conditions as donors of specific, useful morphological and physiological traits to be incorporated in future cultivars.

EARLY SCREENING OF APPLE SEEDLINGS FOR CALCIUM UPTAKE.

Seedling of “Cortland” and “Idared” apples (Malus domestica) were grown in hydroponics and the shoots and roots were evaluated for percent concentration of calcium. “Cortland” is reported to be efficient in calcium uptake in comparison to “Idared”, reputed to be less efficient in calcium uptake and utilization. The seedlings were grown in hydroponic solutions containing calcium ranging from 0.5 ppm to 3.0 ppm concentrations. The shoots and the roots of the seedlings were analyzed for calcium content after 45 days. “Idared” seedling roots and shoots had higher calcium content at 0.5 ppm. However, at 1.5 ppm and at 3.0 ppm “Cortland” seedlings appear to be more efficient at calcium uptake. Early screening may be a useful tool in helping apple breeders select future cultivars that are more efficient at calcium uptake

Inheritance of isozymes in peach x Prunus kansuensis and peach x Prunus davidiana hybrids

Isozyme variation and inheritance were investigated with starch gel electrophoresis in peach (Prunus persica L. Batsch) x P. kansuensis Rehd. and peach x P. davidiana (Carr.) Franch. interspecific hybrids. Of five enzyme systems surveyed for polymorphism, four systems were identified as polymorphic [isocitrate dehydrogenase (IDH, EC 1.1.1.41), phosphoglucomutase (PGM, EC 2.7.5.1), aspartate aminotransferase (AAT, EC 2.6.1.1), and 6 phosphogluconate dehydrogenase (PGD, EC 1.1.1.44)] and may be useful as genetic markers in future cultivar and rootstock development. Analysis of progenies segregating for pairs of loci suggests a possible linkage between the loci coding for Aat-1 and Pgd-2. Independent assortment was observed for isozyme loci Idh/Pgm-2, Idh/Aat-1, Idh/Pgd-2, Pgm-2/Aat-1, Pgm-2/Pgd-2, and Aat-2/Aat-1. The red leaf locus, Gr, assorted independently of the isozyme loci: Idh, Pgm-2, Aat-1, and Pgd-2.

Spread of raspberry bushy dwarf virus by pollination, its association with crumbly fruit, and problems of control

SUMMARYRaspberry bushy dwarf virus (RBDV) was transmitted to raspberry seed both through the pollen and through the ovule and it infected plants pollinated with infected pollen. It did not infect plants prevented from flowering, and transmission through pollen seems to be the only method of spread in the field; in the proximity of infectors, most plants became infected during the first two or three flowering seasons. Plants containing RBDV showed no obvious symptoms, but healthy or infected flowers pollinated with infected pollen produced ‘crumbly’ fruit, containing a high proportion of aborted drupelets. RBDV was difficult to eliminate from infected raspberry by heat therapy. Raspberry cultivars that fail to become infected naturally were also immune to infection by grafting. Use of immune cultivars offers the only method of control and, because infected plants may produce crumbly fruit, future cultivars should if possible possess immunity to RBDV.