Diploid Cultivars Research Articles

Harvest management based on leaf stage of a tetraploid vs. a diploid cultivar of annual ryegrass

AbstractLeaf stage‐dependent defoliation is linked to the plant's physiological status and may be a more suitable criterion than time‐based intervals for harvesting forage grasses, but no reports of research with annual ryegrass (Lolium multiflorum Lam. var. westerwoldicum) were found. To address this, a 2‐year field study was carried out at Raymond, MS, on a Loring silt loam soil (fine‐silty, mixed, thermic Typic Fragiudalfs). Forage production, morphological characteristics and nutritive value responses to defoliation based on leaf stage (2, 3 and 4 leaves per tiller) and two residual stubble heights (RSH; 5 and 10 cm) of a tetraploid (“Maximus”) vs. a diploid (“Marshall”) cultivar of annual ryegrass were quantified. Forage harvested, in 2011, increased linearly as leaf stage increased from 7.3 to 8.8 Mg/ha, but during 2012 was least (7.0 Mg/ha) at 3‐leaf stage and similar at the other two leaf stages (7.6 Mg/ha). Tiller density was less for Maximus (1,191 tillers/m2) than for Marshall (1,383 tillers/m2). Leaf blade proportion decreased with increasing leaf stage and was greater by 9% for Maximus than for Marshall. Generally, forage nutritive value became less desirable with increasing leaf stage. There was a dichotomy in forage harvested and nutritive value responses, but maximum forage productivity was achieved when annual ryegrass was defoliated at the 4‐leaf stage interval.

KARAKTERISASI PISANG REJANG TETRAPLOID HASIL INDUKSI DENGAN ORYZALIN

Triploid banana cultivar is the most desirable cultivar in banana industry because of its higher yield compared to its diploid cultivar. The triploid cultivar can be produced by crossing tetraploid with diploid cultivar. However, tetraploid banana cultivar is rarely existed naturally. Induced tetraploid of Pisang Rejang was produced using oryzalin. The present research was conducted to characterize tetraploid Pisang Rejang (Musa acuminata, AAAA genome) induced by in-vitro oryzalin treatment from diploid Pisang Rejang. Ploidy level, molecular and morphotaxonomic characters were observed. Ploidy identification of induced Pisang Rejang was conducted using Flowcytometer. Molecular characterization was done using RAPD and ISSR markers. Morphology characters were observed based on UPOV (2010). The results showed that tetraploid plants have similar genetic properties with their diploid controls as shown by genetic identity of 0.9901 – 0.9935. The tetraploids were differed from their diploid plants in plan habit and diameter of fruit. The tetraploid plants produce fewer suckers, drooping leaves and broader fruits compared to its diploid control.

Variation in Ploidy and Karyological Diversity in Different Herbaceous Peony Cultivar Groups

The karyotypes of 21 herbaceous peony (Paeonia) cultivars were studied using root tip squashes revealing a wide variety of ploidy levels. There were three tetraploid (2n = 4x = 20), 11 triploid (2n = 3x = 15), and one diploid (2n = 2x = 10) cultivars in the hybrid group; five triploid (2n = 3x = 15) cultivars in the Itoh group; and one diploid (2n = 2x = 10) cultivar in the lactiflora group (LG). The asymmetry index (AI) ranged from 59.61% (‘Cytherea’) to 64.03% (‘Little Red Gem’). The karyotypes of all peony cultivars were 2A with 60% metacentric (m), 20% submetacentric (sm), and 20% subtelocentric (st) chromosomes. The karyotypic background of these 21 herbaceous peony cultivars is discussed in the context of the evolution of ploidy and the three cultivar groups. These results provide cytological information that would assist in a peony hybridization program.

Salt stress reveals differential physiological, biochemical and molecular responses in T. monococcum and T. durum wheat genotypes.

Salt stress responses implicate a complex mechanism and differ from plant species to another. In this study, we analyzed the physiological, biochemical and molecular responses to salt stress of the diploid wheat (T. monococcum) and compared to the tetraploid wheat (T. durum). Our results showed that the diploid wheat cultivar (cv. Turkey) is relatively tolerant to different salt stress conditions than the tetraploid wheat cultivar (cv. Om Rabia3). This tolerance was manifested by significant germination, plant growth and uptake of water generating cell turgor and development. Moreover, total chlorophyll content was higher in the diploid wheat than that in the tetraploid wheat. The Na+ content in leaf blade of the cv. Om Rabia3 was significantly higher than that of the cv. Turkey, suggesting that the diploid cultivar accumulates less toxic sodium in the photosynthetic tissues. This mechanism could be explained by the recirculation of the toxic ions Na+ into the xylem sap by SOS1 protein, which coordinates with HKT-like proteins to reduce the accumulation of Na+ ions in leaf blade. Interestingly, the expression of the three genes SOS1, HKT and NHX was enhanced under salinity especially in leaf blade of the cv. Turkey. Moreover, this wheat cultivar induced the antioxidative enzymes CAT and SOD activity more efficiently than the other cultivar.

The biological characters and polyploidy of progenies in hybridization in 4×–2× crosses in Dianthus caryophyllus

Crosses were carried out between tetraploid Dianthus caryophyllus cv ‘Butterfly’ (2n = 4×= 60) and seven diploid cultivars (2n = 2×= 30). Fewer seeds were obtained and the low seed germination was found which suggested the post-fertilization barrier in 4×–2× crosses. 12 progeny were obtained from 5 crossing combinations. Chromosome analysis revealed that they consisted of 5 triploid hybrid plants and 7 tetraploid hybrid plants, suggesting that unreduced male gamete maybe be involved in polyploid formation. Various flower shapes and colours were observed in the polyploid progenies, showing that sexual polyploidization results in greater variability and fitness. The hybrids obtained by 4×–2× crosses showed the flower-size intermediate between the parents or larger than the parents. Some favourable characters of parents such as flower shape, flower colour and resistance to Fusarium oxysporum, were successfully transmitted to the hybrids. Since polyploid hybrids have some of the profitable characters of the parents, they are expected to be used for future breeding in carnation.

Understanding the genetic diversity and population structure of yam (Dioscorea alata L.) using microsatellite markers.

Yams (Dioscorea sp.) are staple food crops for millions of people in tropical and subtropical regions. Dioscorea alata, also known as greater yam, is one of the major cultivated species and most widely distributed throughout the tropics. Despite its economic and cultural importance, very little is known about its origin, diversity and genetics. As a consequence, breeding efforts for resistance to its main disease, anthracnose, have been fairly limited. The objective of this study was to contribute to the understanding of D. alata genetic diversity by genotyping 384 accessions from different geographical regions (South Pacific, Asia, Africa and the Caribbean), using 24 microsatellite markers. Diversity structuration was assessed via Principal Coordinate Analysis, UPGMA analysis and the Bayesian approach implemented in STRUCTURE. Our results revealed the existence of a wide genetic diversity and a significant structuring associated with geographic origin, ploidy levels and morpho-agronomic characteristics. Seventeen major groups of genetically close cultivars have been identified, including eleven groups of diploid cultivars, four groups of triploids and two groups of tetraploids. STRUCTURE revealed the existence of six populations in the diploid genetic pool and a few admixed cultivars. These results will be very useful for rationalizing D. alata genetic resources in breeding programs across different regions and for improving germplasm conservation methods.

De novo and reference transcriptome assembly of transcripts expressed during flowering provide insight into seed setting in tetraploid red clover

Red clover (Trifolium pratense L.) is one of the most important legume forage species in temperate livestock agriculture. Tetraploid red clover cultivars are generally producing less seed than diploid cultivars. Improving the seed setting potential of tetraploid cultivars is necessary to utilize the high forage quality and environmentally sustainable nitrogen fixation ability of red clover. In the current study, our aim was to identify candidate genes involved in seed setting. Two genotypes, ‘Tripo’ with weak seed setting and ‘Lasang’ with strong seed setting were selected for transcriptome analysis. De novo and reference based analyses of transcriptome assemblies were conducted to study the global transcriptome changes from early to late developmental stages of flower development of the two contrasting red clover genotypes. Transcript profiles, gene ontology enrichment and KEGG pathway analysis indicate that genes related to flower development, pollen pistil interactions, photosynthesis and embryo development are differentially expressed between these two genotypes. A significant number of genes related to pollination were overrepresented in ‘Lasang’, which might be a reason for its good seed setting ability. The candidate genes detected in this study might be used to develop molecular tools for breeding tetraploid red clover varieties with improved seed yield potentials.

Production of Triploid Hydrangea macrophylla via Unreduced Gamete Breeding

Hydrangea macrophylla (Thunb.) Ser., florist’s or bigleaf hydrangea, is the most economically important member of the Hydrangea genus, which accounted for over $120,000,000 in U.S. nursery sales in 2014. Both diploid and triploid H. macrophylla cultivars exist and there is some evidence that triploidy leads to larger plant and floral structures. The diploid cultivar, H. macrophylla ‘Trophee’, was previously shown to have a bimodal pollen size distribution which may be indicative of unreduced gametes. We used H. macrophylla ‘Trophee’ as a parent in a series of crosses with other diploid H. macrophylla cultivars. The objective of this study was to evaluate reciprocal full-sibling H. macrophylla families for ploidy and phenotype, determine the impact of ploidy on phenotype, and determine the efficacy of unreduced gamete breeding. Diploids and triploids were found in the offspring pool with mean 2C genome sizes of 4.5 and 6.7 pg, respectively. All offspring from crosses with ‘Trophee’ as the female parent were diploid as expected. The full-sibling family with ‘Trophee’ as the male parent contained 94% triploids, supporting the hypothesis that the bimodal pollen size distribution of ‘Trophee’ reflects the presence of unreduced male gametes. Triploids had fewer, wider inflorescences than diploids. The stems of triploids were 16% thicker and their leaves were 20% larger than those of diploid full and half-siblings. Triploids had significantly larger stomata (9.0 μm2) than diploids (5.9 μm2). These results establish a link between ploidy and phenotype in plants of similar genetic background and support the efficacy of unreduced gametes in polyploidy breeding.

Growth responses of diploid and tetraploid perennial ryegrass (Lolium perenne) to soil-moisture deficit, defoliation and a root-feeding invertebrate

Growth responses of perennial ryegrass (Lolium perenne L.) diploid cv. Alto and a tetraploid breeding line of Alto infected with wild-type fungal endophyte to three types of stress were studied in a semi-controlled environment. The stresses imposed were: soil-moisture deficit (wilting point vs field capacity), severe defoliation (2.5 vs 6 cm cutting height), and root-feeding invertebrate infestation (nil vs 600 grass grubs (Costelytra zealandica) m–2). Stress treatments were applied simultaneously in a fully factorial design for 8 weeks followed by a 4-week recovery period. Total plant biomass was reduced to a similar extent for both ploidies by soil-moisture deficit (43% reduction), severe defoliation (31% reduction) and root-feeding invertebrates (13% reduction) at the end of the treatment period. At the end of the recovery period, feeding by grass grubs reduced root biomass by 34% and total plant biomass by 25% in the tetraploid cultivar, but there was no effect in the diploid cultivar. Although compensatory growth occurred during the recovery period, one or more aspects of plant growth (e.g. tillering, biomass) remained lower in previously stressed plants at the end of the recovery period. The lower tiller density and total biomass of the tetraploid, in combination with greater allocation of resources to shoot growth and greater susceptibility to root-feeding invertebrates, may compromise its persistence in the field.

Is there a tiller morphology ideotype for yield differences in perennial ryegrass (Lolium perenne L.)?

AbstractThe objectives of this study were to measure the variability in ‘realized’ tiller morphology and identify whether there are emergent generalizations about a tiller ideotype for productivity or survival. Morphological traits during the vegetative growth stage were measured for 2 years in the field for eight perennial ryegrass cultivars: six diploid and two tetraploid cultivars under low and high nitrogen fertilizer (50 and 225 kg N ha−1 year−1 respectively). Traits measured were lamina width, length and area; pseudo‐stem length and diameter; an index of tiller shape; tiller dry weight; tiller density; and herbage mass. Almost all the traits differed significantly between cultivars and significant correlations were found between the 2 years. Principal component analysis identified that tiller morphology and dry‐matter yield were independent. No trait associations indicating alternative cultivar‐specific tiller morphologies were detected but cultivars differed in tiller size. The patterns of change between the 2 years indicated a possible morphological trajectory as swards age. The genetic compensatory relationship between tiller size and density had a 1:1 slope, indicative of constant yield. This implies that larger tillers would be more leafy, and higher leafiness of tetraploid over diploid cultivars was confirmed by the leaf:non‐leaf ratio and tiller shape index.

Reconstructing pedigrees using probabilistic analysis of ISSR amplification

Data obtained from ISSR amplification may readily be extracted but only allows us to know, for each gene, if a specific allele is present or not. From this partial information we provide a probabilistic method to reconstruct the pedigree corresponding to some families of diploid cultivars. This method consists in determining for each individual what is the most likely couple of parent pair amongst all older individuals, according to some probability measure. The construction of this measure bears on the fact that the probability to observe the specific alleles in the child, given the status of the parents does not depend on the generation and is the same for each gene. This assumption is then justified from a convergence result of gene frequencies which is proved here. Our reconstruction method is applied to a family of 85 living accessions representing the common broom Cytisus scoparius.

Innovational trends in apple breeding and fruit quality

The innovational trends in apple breeding include the development of triploid scab immune apple cultivars. The long-term phytopathological and biological studies made it possible to develop approximately 20 first home scab immune apple cultivars and include them in the State Register of Breeding Successes. For the first time in Russia and in the world, the biological and cytoembryological studies favored the development of a number of triploid cultivars that are characterized by high marketability and better biochemical composition of fruit in comparison with well-known old cultivars and diploid scab nonimmune cultivars of VNIISPK breeding.

Development of triploid apple cultivars as a priority in selection

We carried out a detailed examination of the preliminary breeding (prebreeding) techniques during the development of triploid apple cultivars. The characteristics of diploid gamete donors are summarized. It should be noted that at times donors of diploid gametes with the necessary important traits must not only be selected among the existing tetraploid cultivars but also need to be specially bred, in particular, in cases when there are no cultivars and genotypes (donors of diploid gametes) with the given traits in nature. We developed the 30-47-88 apple form (Liberty × 13-6-106) by selection breeding. The 30-47-88 form is at once a donor of diploid gametes and of scab immunity (V f ). During 1970–2015, the following work was carried out on apple breeding using polyploidy: 455 crossing combinations were performed; 660000 flowers were artificially pollinated; 124700 hybrid seeds were obtained; and 47900 one-year-old seedlings were grown, from which, after multiple rejections, 13200 seedlings were planted in breeding orchards. For the first time in Russia, ten apple cultivars (Avgusta, Aleksandr Boiko, Bezhin Lug, Vavilovskoye, Dariona, Maslovskoye, Orlovsky Partizan, Osipovskoye, Patriot, and Yablochny Spas) are developed from intervalence crossings and regionalized. It is stated that apple cultivars developed at the All-Russian Research Institute of Fruit Crop Breeding (VNIISPK) are characterized as a rule by a high level of productivity, better fruit marketability, greater resistance to scab, and higher autogamy. Apple cultivars combining triploidy and scab immunity are developed. Promising breeding work is being performed for apple cultivars combining triploidy, scab immunity, and columnar habit (Co). Brief characteristics are provided for the obtained triploid and scab immune cultivars, Vavilovskoye and Yablochny Spas, developed from intervalence crossings, as well as three triploid cultivars obtained from crossing diploid cultivars. It is noted that triploid apple cultivars developed at VNIISPK are inferior to none of the foreign cultivars, based on a complex of commercial traits, and they significantly excel foreign cultivars in adaptability. Our apple cultivars may contribute to the import substitution of fruit production in Russia.

Comparison of cold hardiness in the leaves of various grape cultivars based on photochemical reflectance index

We compared cold hardiness in the leaves of 12 grape cultivars, including two wild species, two Vitis vinifera × V. labrusca , three HPDs (interspecific crosses) and five V. vinifera L. cultivars using PRI -T curves and analysis of variance (ANOVA). The photochemical reflectance index ( PRI ) of most grape leaves decreased linearly when frozen progressively in darkness, but these patterns varied. The PRI of diploid cultivars and blanc cultivars at the standard temperature ( PRI 4°C) remained relatively steady during exposure to successively lower temperatures (0, -2, -4 and -6°C) compared with polyploid and noir cultivars, representing a boundary dividing grape cultivars into frost tolerant and vulnerable. According to this principle, which was tested by ANOVA, the cold hardiness of the four species was ranked (from high to low) as V. vinifera L. > HPD = wild species > V. vinifera × V. labrusca . The cold hardiness of the 12 cultivars was divided into three classes: Resistant: PRI increased markedly compared with the control, R PRI (( PRI - PRI control )/ PRI control ) > 0 (p < 0.05), indicating high freezing tolerance and wide temperature adaption; Tolerant: PRI changed little compared with the control (p < 0.05), R PRI trended to 0, indicating relative stability when exposed to a short period of freezing temperatures; Vulnerable: PRI decreased dramatically compared with the control, R PRI < 0 (p < 0.05), indicating that photosynthesis was inhibited or damaged due to freezing. We also observed seasonal differences in the cold hardiness of the cultivars; grape leaves were more vulnerable to cold in fall than in spring. This study provides a practical method for estimating cold hardiness in grape.

Pollen Morphology of Herbaceous Peonies with Different Ploidy Levels

The pollen morphology of 26 cultivars of herbaceous peony (Paeonia L.) was examined by scanning electron microscopy (SEM). Pollen grains of the cultivars were mostly subprolate to perprolate, tricolporate, or ellipsoidal in equatorial view, but rounded-trifid in polar view. The poles of pollen grains were mainly flat when viewed in cross-section and only a few appeared to have a circular or arc shape. In addition, the surface of the pollen grains was psilate, and the muri were partly or fully protuberant with a reticulate surface sculpture. However, the shapes and sizes of pollen grains as well as surface ornamentation varied significantly among cultivars with different chromosome numbers. The pollen grains from diploid cultivars were regular and full, and the reticulation holes were evenly distributed, while most of the pollen grains from triploid cultivars were empty flat shells with some heteromorphic pollen whose surface ornamentation was mostly rugulate-reticulate exine. The pollen grains from tetraploid cultivars were the largest although pollen morphology and surface ornamentation differed between Athena and Cream Delight. Six indices [polar axis length (P), equator axis length (E), P/E, pollen perforation diameter (D), ridge width (W), and D/W] were used in Q cluster analysis, which divided the 26 cultivars into three groups. Group I included eight diploid, four triploid, and one tetraploid cultivar. Group II included 12 triploid cultivars with complex genetic backgrounds. Group III included only one tetraploid cultivar Cream Delight. This work may provide an important palynological basis for studying taxonomy and hybrid breeding of herbaceous peony cultivars.

SSR Analysis of Genetic Diversity Among 192 Diploid Potato Cultivars

In potato breeding, it is difficult to improve the traits of interest at the tetraploid level due to the tetrasomic inheritance. A promising alternative is diploid breeding. Thus it is necessary to assess the genetic diversity of diploid potato germplasm for efficient exploration and deployment of desirable traits. In this study, we used SSR markers to evaluate the genetic diversity of diploid potato cultivars. To screen polymorphic SSR markers, 55 pairs of SSR primers were employed to amplify 39 cultivars with relatively distant genetic relationships. Among them, 12 SSR markers with high polymorphism located at 12 chromosomes were chosen to evaluate the genetic diversity of 192 diploid potato cultivars. The primers produced 6 to 18 bands with an average of 8.2 bands per primer. In total, 98 bands were amplified from 192 cultivars, and 97 of them were polymorphic. Cluster analysis using UPGMA showed the genetic relationships of all accessions tested: 186 of the 192 accessions could be distinguished by only 12 pairs of SSR primers, and the 192 diploid cultivars were divided into 11 groups, and 83.3% constituted the first group. Clustering results showed relatively low genetic diversity among 192 diploid cultivars, with closer relationship at the molecular level. The results can provide molecular basis for diploid potato breeding.

Collecting banana diversity in eastern Indonesia

Major diseases, including Fusarium wilt tropical race 4, threaten banana production systems worldwide. New sources of genetic resistance are considered necessary in the fight against such diseases. The triangular region of Indonesia taking in Sulawesi, the Maluku Islands and Lesser Sunda Islands was prioritized by the Global Musa Genetic Resources Network, MusaNet for exploration and collecting. It is just east of the Wallace Line, which is recognized as a transition zone for flora in southeast Asia, and had been little explored. Bioversity International funded a team of scientists from Indonesia and Australia to make collecting missions in the triangle in October 2012 and February 2013. Suckers and seeds of 35 promising new accessions were collected. About 90% of these are either wild species or diploid cultivars of more direct use to breeding programs. These were morphologically characterized during the collecting missions and included a set of photographs recommended by Bioversitys Taxonomic Advisory Group. Cigar leaf samples were also collected and sent as fresh samples to the International Banana Genotyping Centre in the Czech Republic. Ploidy and DNA (SSR) genotyping determinations from these samples have been invaluable in quickly interpreting and better appreciating what has been discovered. The new accessions have been grown on at Solok field collection, West Sumatra and will be made available by Indonesia to the international community, including breeding programs, for evaluation and utilization. Information on wild Eumusa prompts a rethinking of the phytogeography of Musa acuminata. The variation within the Australimusa species M. lolodensis highlights the need for broader study of this Musa section. French Plantain-like edible AAs and prospects for the generation of African plantains in the region were identified. The mission indicated existence of local edible ABs in eastern Indonesia in association with balbisiana hybrids origins in the region. Further explorations in the region should add to Musa diversity knowledge.

Competitive dynamics in mixtures of perennial ryegrass cultivars during two growing seasons under two cutting managements

Cultivar mixtures of perennial ryegrass (Lolium perenne L.), which mostly contain both diploids and tetraploids, are widely used in agricultural grassland systems, and yet limited knowledge exists on their competitive interactions after sowing. Two diploid cultivars (AberMagic, Twystar) and a tetraploid (Greengold), sown in different binary mixture ratios, were monitored over a 2-year period under frequent cutting to simulate cattle grazing and conservation managements. Composition was determined from fluctuations in phosphoglucoisomerase allozyme frequencies relative to the frequencies of the component cultivars. An interaction occurred between cultivar sown ratio and seasonal period whereby greater changes in proportions occurred early in the first year. Cultivar proportions were significantly influenced by sown ratio, seasonal period and management. The diploid mixtures remained similar to their sown ratios, whereas the diploid–tetraploid mixtures, sown at 15% and 30%, increased to 33–61% under simulated grazing and 40–59% under conservation use. No changes were observed in the 50 : 50 diploid–tetraploid mixtures. A competitive equilibrium was attained after 1 year and compositions remained stable throughout the second year. The differences in large canopy structure between ploidies are a likely factor affecting competitive ability, and mixture construction should account for these hierarchies to achieve the desired sward composition.

Advances in table grape breeding in Japan.

In Japan, few grape cultivars related to Vitis vinifera existed 200 years ago, on account of Japan’s high rainfall. Many V. labruscana and vinifera cultivars were introduced to Japan in the 19th century. Labruscana was grown instead of vinifera, mainly because of severe disease problems and a high incidence of berry cracking. Grape breeding for table use started in the 20th century, with the goal of combining the berry quality of vinifera with the ease of cultivation of labruscana. By 1945, three strategies were used: 1) crossing among introduced diploid vinifera and vinifera-related cultivars of Japanese origin, 2) interspecific crossing in tetraploid cultivars, and 3) interspecific crossing in diploid cultivars, resulting in ‘Neo Muscat’, ‘Kyoho’, and ‘Muscat Bailey A’. Later, tetraploid interspecific crossing over generations developed many ‘Kyoho’-related cultivars, including ‘Pione’, many of which have large berries, intermediate flesh texture between the two species, a labruscan or neutral flavor, and moderate disease resistance. Interspecific diploid crossing over generations developed ‘Shine Muscat’ in 2006, with large berries, crispy flesh, a muscat flavor, no cracking, seedless fruit by gibberellin application, and moderate resistance to downy mildew and ripe rot.

Ground Cover Assessment of Perennial Ryegrass Using Digital Imaging

Ground‐cover assessments of grassland swards provide information on durability and persistence, which in turn relate to disease resistance and competitive ability. These assessments are traditionally performed visually, but digital imaging can provide a more accurate method of ground‐cover scoring. Differences in ground cover between late‐heading perennial ryegrass (Lolium perenne L.) cultivars in four trials (2 yr of sowing and two sites) were determined using both digital imaging and visual scoring. Ground‐cover percentages were calculated from digital images with public‐domain software on the basis of color separation of grass leaves from bare soil. For both years of sowing, highly significant interactions of cultivar and site were detected. Significant differences between cultivars were detected in three out of four trials, with diploid cultivars having greater cover than tetraploids in the older trials. Thus digital image analysis of ground cover may be a useful tool in crop improvement and provision of guidelines regarding suitability of a particular cultivar for a particular site.