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Yu Cui, Jinsheng Wang, Xingchun Wang, and Yiwei Jiang

Perennial ryegrass (Lolium perenne L.) is a popular cool-season forage and turfgrass in temperate regions. Due to its self-incompatible and out-crossing nature, perennial ryegrass may show a high degree of heterozygosity. Perennial ryegrass generally is susceptible to drought stress, but variations of drought response of individual genotypes within a particular accession or cultivar are not well understood. The objective of this study was to characterize phenotypic diversity of drought tolerance within and among accessions in relation to genetic diversity in perennial ryegrass. Five individual genotypes from each of six accessions varying in origin and growth habits were subjected to drought stress in a greenhouse. Leaf wilting, plant height, chlorophyll fluorescence (Fv/Fm) and leaf water content (LWC) differed significantly among accessions as well as among genotypes within each accession under well-watered control and drought stress conditions. Fv/Fm was highly correlated with LWC under drought stress. Genetic diversity among and within accessions were identified by using previously characterized 23 simple sequence repeat markers. Across accessions, the mean major allele frequency, gene diversity, and heterozygosity values were 0.66, 0.43, and 0.66, respectively. Accessions with closer genetic distance generally had similar drought responses, while accessions with greater genetic distance showed distinct drought tolerance. Significant differences in drought tolerance among and within accessions, especially for individual genotypes within one accession, indicated that variations of drought response could be used for enhancing breeding programs and studying molecular mechanisms of stress tolerance in perennial ryegrass.

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Jaladet M.S. Jubrael, Sripada M. Udupa, and Michael Baum

Currently, the identification and characterization of date palm varieties rely on a small number of morphological traits, mainly of fruit, which are complex and greatly influenced by the environment. As a result, different varietal names may actually refer to the same variety while different varieties may have the same name. Therefore, new descriptors like molecular markers are required to identify, characterize, and estimate genetic diversity in this crop. Here we used amplified fragment length polymorphism (AFLP) markers to discriminate 18 Iraqi date palm varieties and to estimate the genetic relationship among the varieties. A total of 122 polymorphic AFLP loci were scored, with an average of 17.4 polymorphic loci per primer combination. The use of any one of the four combinations, P101(aacg)/M95(aaaa), P74(ggt)/M95(aaaa), P73(ggg)/M95(aaaa), or P100(aacc)/M95(aaaa), was sufficient to uniquely identify all the varieties. Jaccard's genetic similarity index ranged from 0.108 to 0.756, indicating moderate to diverse relationships. Estimation of average proportion of fixed recessive AFLP loci indicated that most of the loci in variety `Chipchab' were fixed, whereas most of the loci in `Jamal Al-Dean' could be heterozygous and in-between in other varieties. Unweighted pair group method with arithmatic mean (UPGMA) analysis ordered the date palm varieties first into two broad groups at 27% similarity levels. One group consisted of seven varieties and the second group consisted of the remaining 11 varieties of date palm. These results showed that the AFLP technique is an efficient method for varietal identification and estimating genetic relationships in date palm.

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Ryan S. Donahoo and Kurt H. Lamour

isolates of P. citrophthora are not known at this time. Although genotypic diversity was present within all the species studied except P. foliorum , we were also able to document the spatiotemporal persistence of isolates carrying identical multilocus

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Deborah Pagliaccia, Georgios Vidalakis, Greg W. Douhan, Ramiro Lobo, and Gary Tanizaki

, there was also genotypic diversity within putatively named varieties. This is not surprising because outcrossing can occur. Moreover, relative ease of propagation has made pitahaya a popular plant among hobby breeders and backyard growers, which has

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Isabelle Y. Delannay, Jack E. Staub, and Jin Feng Chen

The genetic base of commercial cucumber (Cucumis sativus L.) is extremely narrow (about 3%–8% polymorphism). Wide-based crosses within C. sativus [i.e., C. sativus var. sativus × C. sativus var. hardwickii (R.) Alef.] and interspecific hybridization attempts before 1995 have not substantially increased genetic diversity for plant improvement. However, in 1995, an amphidiploid (Cucumis hytivus Chen and Kirkbride) was derived from a C. sativus × Cucumis hystrix Chakr. mating. A derivative of this amphidiploid was used herein to broaden the genetic base of cucumber through backcross introgression [(C. sativus × C. hytivus) × C. sativus]. Initially, the combining ability of eight genetically diverse lines was investigated for days to anthesis (DA), sex expression (SEX), lateral branch number (LBN), fruit per plant (FP), fruit length:diameter ratio (L:D), and salt-processing ability [i.e., processed fruit color (exterior and interior), shape, and seed cavity characteristics]. Based on the combining ability, inbred backcross lines [IBL (BC2S3)] were developed from an original gynoecious determinate line WI 7023A [C. sativus (recurrent parent)] × monoecious indeterminate line WI 7012A (C. sativus × C. hytivus derived) mating, where 30 of 392 (8%) BC1 progeny were selected based on their diversity at 16 mapped marker loci. These progeny were used to develop BC2 progeny, which were then self-pollinated without further selection to produce 94 IBL. These IBL were genotyped and evaluated in the open field in two plantings in 2008 for DA, SEX, LBN, leaf size, FP, and L:D. The genetic distance (GD) between parental lines was 0.85, and the GD among IBL ranged between 0.16 and 0.75. Multivariate analyses indicated that IBL differed from parental lines and possessed considerable morphological and genotypic diversity that could be used to broaden the genetic base of commercial U.S. processing cucumber.

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Pan-Hui Huang, Wen-Bin Yu, Jun-Bo Yang, Hong Wang, and Lu Lu

.730). The deviation from HWE could be attributed to the low genotypic diversity caused by self-pollinated breeding system ( Li et al., 2005 ) or limited sampling of P. rex (only 22 individuals evaluated). Huang et al. (2008) developed 11 microsatellites

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Paul W. Bosland and Danise Coon

-Burruezo, A. Kollmannsberger, H. Gonzalez-Mas, M.C. Nitz, S. Nuez, F. 2010 HS-SPME comparative analysis of genotypic diversity in volatile fraction and aroma contributing compounds of Capsicum fruits from the annuum-chinense-frutescens complex J. Agr. Food

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Paul W. Bosland and Danise Coon

-Burruezo, A. Kollmannsberger, H. Gonzalez-Mas, M.C. Nitz, S. Nuez, F. 2010 HS-SPME comparative analysis of genotypic diversity in volatile fraction and aroma contributing compounds of Capsicum fruits from the annuum-chinense-frutescens complex J. Agr. Food

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Paul W. Bosland

frutescens HortScience 42 16 19 Rodriguez-Burruezo, A. Kollmannsberger, H. Gonzalez-Mas, M.C. Nitz, S. Nuez, F. 2010 HS-SPME comparative analysis of genotypic diversity in volatile fraction and aroma contributing compounds of Capsicum fruits from the annuum

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Sarah J. Pethybridge, Niloofar Vaghefi, and Julie R. Kikkert

beticola populations from table beet fields in New York have an equal distribution of the two mating type alleles and high genotypic diversity ( Vaghefi et al., 2016 , 2017a , 2017b ) consistent with observations suggestive of the presence of cryptic sex