Buffalograss resistance to mealybugs: Germplasm evaluation, mechanisms, and inheritance

Buffalograss, Buchloe dactyloides (Nutt) Engelm, is receiving attention as an alternative turfgrass species because of its drought tolerance and low maintenance requirements. The University of Nebraska is conducting research on the breeding, management, and potential pests of buffalograss. Two insects known to cause injury are the mealybugs Tridiscus sporoboli (Cockerell) and Trionymus sp. This project investigated the potential of developing buffalograss cultivars with improved resistance to mealybugs. Dramatic differences in resistance to mealybugs were found among buffalograss selections in greenhouse and field screening trials. Cultivars \u27Prairie\u27 and \u27609\u27, and several experimental selections showed excellent resistance to mealybugs; most selections were moderately susceptible; and a few selections, such as 85-97, were highly susceptible. Initial observations of highly resistant selections revealed glabrous leaves. Therefore, selections were evaluated for pubescence and significant positive correlations were found between pubescence and mealybug susceptibility. Pubescence ratings correlated with trichome counts, which ranged from 0-11 trichomes per mm\sp2. Scanning electron microscopy studies suggested that pubescence may provide a framework for the waxy ovisac and a foothold for mobile early-instar nymphs. In preliminary choice trials, mealybugs did not exhibit a preference for susceptible 85-97 over resistant \u27609\u27. To study inheritance of resistance and pubescence, progeny of 20 genotypes were evaluated and significant differences were found among half-sib families. Relatively high heritabilities were estimated for mealybug resistance using maternal half-sib analysis ({\rm h\sp2\sb{m} = 0.87}) and offspring-parent regression ({\rm h\sp2\sb{op} = 0.56}). Heritability estimates for leaf pubescence were {\rm h\sp2\sb{m} = 0.59} and {\rm h\sp2\sb{op} = 0.28}. Less than 1% of progeny had glabrous leaves, suggesting a simply inherited recessive trait. A non-significant correlation ({\rm r\sp2 = 0.06}) was found between pubescence and mealybug susceptibility of progeny. Since numerous pubescent plants were resistant, additional factors are likely involved in resistance to mealybugs. The 119 plants which showed no signs of mealybug infestation (10% of total evaluated) were grown in an isolated crossing block and seed was harvested. Progeny from 16 of these plants were evaluated and 359 (43% of total) were free of mealybugs. This high percentage of mealybug-resistant progeny was consistent with the high heritabilities previously estimated. Highly resistant families are suggested for use in the development of a seeded mealybug-resistant buffalograss cultivar

Identification of Mealybug- (Homoptera: Pseudococcidae) Resistant Turf-Type Buffalograss Germplasm

Two species of mealybugs, Tridiscus sporoboli (Cockerell) and Trionymus sp., have emerged as potentially serious pests of turf-type buffalograss, Buchloë dactyloides (Nuttall) Engelmann. Sixty-two buffalograss selections were screened for resistance to these mealybugs in 4 greenhouse trials. Using a 1-6 rating scale (1 = no signs of mealybugs, 6 = \u3e75% of tillers infested), \u27Prairie\u27 and \u27609\u27 showed high levels of resistance to mealybugs, whereas several experimental selections, including 90-157,84-512 and 84-412, exhibited moderate resistance. Most selections were moderately susceptible, and 85-97 was highly susceptible with almost every tiller infested and plants near death. In field tests, mealybug infestations were highly variable, both within and among plots. However, in most cases, selections evaluated in the field showed similar responses as in greenhouse trials. Pubescence was positively correlated with buffalograss susceptibility to mealybugs. A glabrous leaf surface is suggested as a possible mechanism of resistance

United States Patent: Buffalograss Plant Named ‘NE86-120’

A vegetatively reproduced buffalograss cultivar named \u27NE86-120\u27 is distinguished from other commercially produced buffalograss varieties by its excellent turfgrass color, cold tolerance, high density, dark green color, low growth habit, and rate of establishment. \u27NE86-120\u27 is also distinguished from other varieties by molecular markers and nuclear DNA content. \u27NE86-120\u27 is suitable for use in low to medium maintenance situations in arid and semi-arid climates of United States and Canada

United States Patent: Buffalograss Plant Named ‘NE91-118’

A vegetatively reproduced buffalograss cultivar named \u27NE91-118\u27 is distinguished from other commercially produced buffalograss varieties by its excellent turfgrass color, cold tolerance, high density, low growth habit, and rate of establishment. \u27NE91-118\u27 is also distinguished by molecular markers and nuclear DNA content. \u27NE91-118\u27 is suitable for use in low to medium maintenance situations in arid and semi-arid climates of United States and Canada

Evaluation of Buffalograss Leaf Pubescence and Its Effect on Resistance to Mealybugs (Hemiptera: Pseudococcidae)

Considerable progress has been made in improving the turfgrass characteristics of buffalograss, Buchloë dactyloides (Nutt) Engelm, a native North American grass species with low maintenance requirements (Riordan et al., 1993). Two mealybugs, Tridiscus sporoboli (Cockerell) and Trionymus sp. (Hemiptera: Pseudococcidae) have emerged as buffalograss pests (Baxendale et al., 1994). Mealybugs have been associated with buffalograss stands throughout Nebraska (Baxendale et al., 1994), as well as in Texas and Arizona. Unfortunately, the Pseudococcidae are poorly described and species identification requires extensive specimen preparation (Ferris, 1950, 1953). Buffalograss mealybugs have an oblong, pale purple-grey, membranous body, ranging in length from 0.2 to 3.0 mm. They are covered with cottony wax secretions (Baxendale et al., 1994). The adult female is relatively immobile and is found inside or near the leaf sheath, or behind the leaf axils enclosing the female flower. Clusters of eggs are deposited within a filamentous waxy ovisac. First instars, or crawlers, migrate to new feeding sites and likely play a role in host selection (McKenzie, 1967). Mealybugs are often overlooked in the field because of their small size and hidden location on the plant (Baxendale et al., 1994). Severe mealybug infestations result in a general decline of the buffalograss stand, which can be confused with drought or other stresses. Initially, the turf takes on a reddish-purple discoloration, followed by browning and thinning. A close examination will reveal the mealybug’s white cottony secretions. Possible strategies for managing mealybugs on buffalograss include pesticides, biological control, and use of resistant buffalograsses. Developing mealybug-resistant buffalograsses is of particular importance because this grass is used primarily as a low-input turfgrass species. Fortunately, several resistant buffalograsses have been identified (Johnson-Cicalese et al., 1998). Understanding the mechanism of this resistance would be helpful for formulating optimal strategies for identifying and exploiting new sources of resistance. While considerable progress has been made in identifying germplasm resistant to insect pests, progress toward characterization of the mechanisms conferring the resistance has been limited

United States Patent: Buffalograss Plant Named NE86-61

A vegetatively reproduced buffalograss cultivar named NE86-61 is distinguished from other commercially produced buffalograss varieties by its excellent turfgrass color, cold tolerance, high density, dark green color, low growth habit, and rate of establishment. NE86-61 is also distinguished from other varieties by molecular markers and nuclear DNA content. NE86-61 is suitable for use in low to medium maintenance situations in arid and semi-arid climates of United States and Canada

Identification and mapping of fruit rot resistance QTL in American cranberry using GBS

Abstract: Sustainability of the cranberry industry is threatened by widespread and increasing losses due to fruit rot in the field, as well as increasing restrictions on fungicide inputs. Breeding for resistance offers a partial solution, but is challenging because fruit rot is caused by a complex of pathogenic fungi that can vary by location and from year to year. We identified four genetically diverse germplasm accessions that exhibit broad-spectrum fruit rot resistance under field conditions. Three of these accessions were used in biparental crosses to develop four populations segregating for resistance. Genotyping by sequencing was used to generate SNP markers for development of high density genetic maps and QTL analyses. Nineteen QTL associated with fruit rot resistance, distributed on nine linkage groups, were discovered in our populations. Three of these QTL matched previously reported fruit rot resistance QTL. Four newly reported QTL found on linkage group 8 (Vm8), which explain between 21 and 33% of the phenotypic variance for fruit rot, are of particular interest to our breeding program. The populations described herein were also phenotyped for other horticulturally important traits, and QTL associated with yield and berry weight were identified. These QTL provide markers for candidate gene discovery and for future breeding efforts to enhance and pyramid disease resistance and other traits into elite horticultural backgrounds

Performance of Welker, Haines and other advanced selections in regional trials

Abstract. The objective of this study was to assess advanced selections from Rutgers cranberry breeding program, along with recently released cultivars, for their performance in different cranberry growing regions. Results are presented from trials in New Jersey, Wisconsin, Oregon, and Washington. The trials were evaluated for plant vigor, yield, berry weight, fruit rot, other relevant diseases, and fruit chemistry (TAcy, Brix, titratable acidity and proanthocyanidin). Differences were found between locations in cranberry performance. Fruit in the Pacific Northwest (PNW) is smaller (a trial mean of 1.3g/berry) compared to NJ (2.3g). The Oregon trial had the highest mean TAcy (73mg/100g fruit) and Brix (10.1% soluble solids) of any growing region. Wisconsin trials typically exhibit the highest yields. Although highly variable, Wisconsin also had less fruit rot (a trial mean of 4.4% rotted fruit), especially compared to New Jersey (35%). Differences were apparent between locations in cultivar performance as well. Welker, for example, had exceptional establishment and high early yields, but was more susceptible to fruit rot and would not be as well suited to the Northeast. Our breeding program continues to address the changing needs of the cranberry industry, including increasing fruit rot resistance (FRR), climatic adaptation (heat stress), and varieties suited for current major products, e.g., sweetened dried cranberries (SDC). For example, the fruit color criteria has changed for some SDC’s processes (i.e. very high Tacy is unacceptable), making later ripening selections such as NJS98-11 better suited for high TAcy growing regions, e.g., PNW. In Oregon, NJS98-11 had a mean TAcy of 28mg/100g fruit, compared to Stevens at 70mg/100g FW or Scarlet Knight, 191mg/100g FW. Increasing fungicide restrictions and fruit rot pressure has made the development of FRR cultivars a high priority. Promising first generation FRR breeding selections have been developed and are performing well in WA, WI, and NJ trials. Second and 3rd breeding cycle populations derived from FRR selections have now been planted in three locations

United States Patent: 315 Buffalograss

A vegetatively reproduced buffalograss cultivar, named 315 Buffalograss, is distinguished by its excellent dark green color, high density, low growth habit, drought resistance, heat and cold tolerance, wear tolerance, low maintenance requirements and slow rate of establishment

Multivariate GBLUP Improves Accuracy of Genomic Selection for Yield and Fruit Weight in Biparental Populations of Vaccinium macrocarpon Ait

<p>The development of high-throughput genotyping has made genome-wide association (GWAS) and genomic selection (GS) applications possible for both model and non-model species. The exploitation of genome-assisted approaches could greatly benefit breeding efforts in American cranberry (Vaccinium macrocarpon) and other minor crops. Using biparental populations with different degrees of relatedness, we evaluated multiple GS methods for total yield (TY) and mean fruit weight (MFW). Specifically, we compared predictive ability (PA) differences between univariate and multivariate genomic best linear unbiased predictors (GBLUP and MGBLUP, respectively). We found that MGBLUP provided higher predictive ability (PA) than GBLUP, in scenarios with medium genetic correlation (8–17% increase with cor_g~0.6) and high genetic correlations (25–156% with cor_g~0.9), but found no increase when genetic correlation was low. In addition, we found that only a few hundred single nucleotide polymorphism (SNP) markers are needed to reach a plateau in PA for both traits in the biparental populations studied (in full linkage disequilibrium). We observed that higher resemblance among individuals in the training (TP) and validation (VP) populations provided greater PA. Although multivariate GS methods are available, genetic correlations and other factors need to be carefully considered when applying these methods for genetic improvement.</p