Assessing Rosa persica genetic diversity using amplified fragment length polymorphisms analysis

The genetic diversity among 128 Iranian Rosa persica (R. persica) accessions in the different populations was analyzed. Amplified fragment length polymorphisms (AFLP) technique was used to produce 171 polymorphic fragments. The number of polymorphic loci ranged from 101 to 147 and the polymorphism information content (PIC) varied from 0.289 to 0.073, with an average of 0.16. This shows extreme variability and genetic diversity among the studied R. persica populations. An indirect estimate of the number of migrants per generation (Nm = 0.376) indicated that gene flow was relatively low among populations of the species. Cluster analysis using the UPGMA method grouped all accessions into six clusters. The results did not show relative agreement with the genotypes’ region of origin. Based on an analysis of molecular variance, 48% of the genetic variation of R. persica was within population and 52% was among populations. The present analysis revealed that Iranian R. persica genotypes are highly variable and genetically distinct from their origins. The apparent unique nature of the R. persica genotypes revealed by our results supports the case for the implementation of more intense characterization and conservation strategies, and provides useful information to address breeding programmes and germplasm resource management in Rosa spp.     

Development of novel EST-SSR markers for cucumber (Cucumis sativus) and their transferability to related species

We report on the development of novel simple sequence repeat (SSR) markers from publicly available Cucumis sativus expressed sequence tags (ESTs) and on their transferability among related species. In total, 533 di- to penta-type SSRs were identified from 6344 cucumber ESTs retrieved from GenBank. Identified SSRs mainly comprised of di- and tri-nucleotide repeats, of which AG and AAG motifs were much abundant. A total of 392 SSR-containing unigenes (non-redundant ESTs/consensus sequences) were suitable for primer design. From these, 35 primer pairs were designed as representative samples and 28 were usable markers. Twenty-six out of 28 usable markers revealed polymorphism among 21 cucumber accessions with 2–7 alleles detected (mean = 3.77) and their polymorphism information content (PIC) values ranged from 0.091 to 0.748 (mean = 0.388). The polymorphism observed herein partially arose from the null alleles which occurred at the multiple homoeoloci detected by the markers. Transferability of the 28 EST-SSR markers was investigated in four other cucurbits: melon, watermelon, pumpkin and gourd which showed frequency of 92.9%, 57.1%, 53.6% and 60.7%, respectively. The EST-SSR markers developed herein will complement the currently available genomic SSR markers and may be useful for genetic studies in cucumber and related species.     

Novel genomic and EST-derived SSR markers in Japanese chestnuts

A total of 366 novel simple sequence repeat (SSR) markers were developed in Japanese chestnut (Castanea crenata), comprising 220 genomic SSRs derived from enriched genomic libraries and 146 expressed sequence tag (EST)–SSRs obtained from large-scale EST sequencing analysis. Thirty accessions, comprising Japanese, Chinese (C. mollissima), European (Castanea sativa), and American chestnuts (Castanea dentata), were used for evaluation of SSR polymorphism and transferability across species. The EST–SSRs showed less polymorphism than the genomic SSRs and were more transferable. The mean observed heterozygosity (H_O) and the mean expected heterozygosity (H_E) of genomic SSRs in the Japanese chestnuts were 0.63 and 0.68, respectively; those of EST-SSRs were each 0.47. Although about 80% of the genomic SSRs were amplified in all 4 species, more than 95% of the EST–SSRs were transferable across all 4 species. The many novel SSRs developed in this study will be applicable for the construction of genetic linkage maps, QTL analysis of phenotypic traits, high-throughput genotyping of marker-assisted selection, and association genetics.     

Modeling individual leaf area of ginger (Zingiber officinale Roscoe) using leaf length and width

Leaf area estimation is an important biometrical observation one has to do for comparing plant growth in field and pot experiments. In this study, a leaf area estimation model was developed for ginger (Zingiber officinale Roscoe), using linear measurements of leaf length (L) and maximum width (W). Leaves from five ginger varieties (Varada, Rejatha, Mahima, Maran and Himachal) were used to develop the model in 2006–2007. The actual leaf area (LA) was measured with a leaf area meter (LI-3100, LI-COR, Lincoln, NE, USA) and taken as reference LA. The linear measurements were used to build linear (LA = a + b × L × W) and power models (LA = α × (L × W)^β) for each variety, as the modeling among variety were not different from each other, data for all five varieties have been pooled and compared with earlier models by graphical procedures and statistical criteria such as Mean Square Error (MSE), Root Mean Square Error (RMSE) and Chi-square (χ²). The selected model was validated during 2007–2008. The validation data set was used to produce a validation model for each variety by re-estimating the model parameters to develop the estimation model and the models were compared for consistency. The predicted LA (PLA) was compared with observed LA (OLA) by graphical procedures and lack of agreement was evaluated by calculating the relative bias, estimated by the mean of differences (d) and the standard deviation (SD) of the differences. Normality test was carried out by Spearman's rank correlation coefficient (r_s) and residuals were normally distributed. Finally, the proposed model for leaf area estimation of ginger is LA = −0.0146 + 0.6621 × L × W, R² = 0.997. This model can be reliably used for estimating leaf area of ginger non-destructively. The same equation can be extrapolated to all varieties and land races of ginger as it is vegetatively propagated crop with narrow genetic variability.     

Inter- and intra-specific genetic diversity among cyclamen accessions investigated by RAPD markers

Random amplified polymorphic DNA (RAPD) analysis was used to characterize genetic diversity of 26 Cyclamen persicum and Cyclamen com accessions. Eighty-four arbitrary primers tested, among which nine primers showed reliable polymorphic banding patterns and yielded 104 polymorphic markers. Jaccard's similarity coefficient among accessions ranged from 0.99 to 0.08. At a similarity of 68%, accessions were divided into three clusters. The cophenetic correlation coefficient between the similarity matrix and the dendrogram was relatively high (r = 0.9) showing the goodness of fit of the dendrogram. The RAPD analysis offered a rapid and reliable tool for the estimation of inter- and intra-specific variability in cyclamens. The wide genetic variation observed for cyclamens within Iran guarantees a promising future of breeding.     

Comparative analysis of genetic diversity in Tunisian apricot germplasm using AFLP and SSR markers

Eighty-one accessions representing apricot germplasm in Tunisia were collected from different areas of cultivation and fingerprinted using amplified fragment length polymorphism (AFLP) and microsatellites (SSR) markers. A total of 339 polymorphic markers were revealed using 5 AFLP primers combinations and 24 SSR loci. AFLP and SSR markers expressed a high level of polymorphism allowing the distinction of the accessions with an efficiency coefficient of discrimination of 100% for AFLP and 97% for SSR markers. Genetic diversity structure was assessed with AFLPs and SSRs markers separately then with combined matrix data by the help of hierarchical clustering elaborated using Wards method based on Nei and Li (1979) distances. Comparison of the obtained dendrograms revealed a phylogeographic structure into two major groups with significant conservation between the observed subgroups in relation with the geographic origin of the accessions. The relative efficiency of the markers in determining the genetic relationships among apricot accessions has been assessed and a combination of AFLPs and SSRs markers was the most effective. In addition, Mantel test based on genetic distances indicated highly significant correlation between AFLP-SSR data and each of the AFLP and SSR ones, with Pearson correlation values of r = 0.873 and r = 0.692, respectively, revealing the higher efficiency of the combination of both molecular techniques (AFLP and SSR) to estimate the levels of genetic variability among apricot germplasm.     

Variety identification and comparative analysis of genetic diversity in yardlong bean (Vigna unguiculata spp. sesquipedalis) using morphological characters,SSR and ISSR analysis

Genetic diversity and relatedness of 23 yardlong bean (Vigna unguiculata spp. sesquipedalis) accessions and 7 accessions of a hybrid between cowpea (V. unguiculata spp. unguiculata) and yardlong bean (dwarf yardlong bean) in Thailand were estimated using morphological characters, simple sequence repeat (SSR) and inter-simple sequence repeat (ISSR) markers. In addition, two mungbean (Vignaradiata (L.) Wilczek) and two blackgram (Vigna mungo (L.) Hepper) accessions were also used as outgroup species for molecular analysis. Five morphological characters were diverse among most accessions. However, five groups of 2–3 accessions could not be distinguished from one another based on these morphological characters alone. Unweighted pair-group arithmetic average (UPGMA) analysis of these characters separated these 30 accessions into 2 major groups; the yardlong bean group and the dwarf yardlong bean group. Eleven of the sixteen SSR primers yielded clear SSRs, ten of which were polymorphic (90.91% polymorphism), detecting a total of 54 alleles with an average of 4.91 alleles per locus. These 10 polymorphic SSR markers successfully distinguished 28 yardlong bean and dwarf yardlong bean accessions. The polymorphic information content (PIC) among genotypes varied from 0.251 to 0.752 with an average of 0.597. Among the 16 ISSR primers used, a total of 312 ISSR fragments were amplified for these three Vigna species, revealing the polymorphism percentage of 91.03%. The average ISSR PIC value (0.197) with the range of 0.137–0.276 was lower than that of SSR. Nevertheless, the average marker index of this multilocus marker was 3.495, which was higher than that of SSR (0.669), owing to the differences in the effective multiplex ratio. In addition, Mantel test cophenetic correlation coefficient was higher for ISSR (0.566) than that of SSR (0.198). These results indicated higher efficiency of ISSR for estimating the levels of genetic diversity and relationships among yardlong beans and dwarf yardlong beans in this study. Pair-wise coefficients of SSR- and ISSR-based genetic similarity among all yardlong bean and dwarf yardlong bean accessions averaged 0.87 and 0.91, respectively, suggesting a narrow genetic base that emphasizes the need to broaden genetic diversity to ensure continued breeding success. Clustering of genotypes within groups was not similar when SSR and ISSR derived dendrograms from UPGMA analysis were compared. It appeared that ISSR was the most effective marker system in determining the genetic variability and relationships among yardlong bean and dwarf yardlong bean accessions and differentiating three Vigna species. In addition, ISSR was also most useful for variety identification since all 30 yardlong beans and dwarf yardlong bean accessions can be effectively distinguished by only four ISSR primers with the highest PIC values.     

Development of new microsatellite markers for molecular diversity analysis of Citrus species

Summary

Thirty microsatellite loci for further genetic analysis of Citrus species were developed by constructing a microsatellite-enriched library using capture with streptavidin-coated magnetic beads and used to assess genetic diversity in 40 Citrus accessions. In total, 150 alleles were detected, with an average of five alleles per locus. The average gene diversity and polymorphism information content values were 0.58 and 0.52, and ranged from 0.35 – 0.74 and from 0.32 – 0.70, respectively. Values for the observed and expected heterozygosities ranged from 0.13 – 1.00 and from 0.36 – 0.75, respectively. Fifteen loci deviated from the Hardy-Weinberg equilibrium (P < 0.05). The mean similarity coefficient among accessions was 0.5906. Based on the UPGMA algorithm, two main groups were successfully identified. These new microsatellite markers can be used to further investigate the genetics of, and phylogenic relationships in Citrus spp.     

Genetic diversity and population genetic structure of pomegranate (Punica granatum L.) in Iran using AFLP markers

Pomegranate (Punica granatum L.) is one of the oldest known edible fruits. It is native to Iran and spread from Iran to other areas. In this study amplified fragment length polymorphism (AFLP) was used to detect intra- and inter-population genetic diversity of pomegranate. A group of 67 accessions belonged to 4 populations from Iran was studied using eight primer combinations. A total of 221 scorable bands were amplified, of which, 118 (54.13%) were polymorphic. Resolving power (Rp) ranged from 5.70 to 9.21, and the average of polymorphism information content (PIC) per primer pair was 0.40. According to Nei's gene diversity and allelic statistics, Isfahan population had a highest genetic diversity (H = 0.3646, I = 0.5327, N_e = 1.6467). Coefficient of gene differentiation between populations (GST) was 0.124, indicated that mainly proportion of genetic variation (87.6%), was within populations and the remaining (12.4%) of the variation was among populations that, also supported by analysis of molecular variance (AMOVA). The gene flow (Nm) varied from 0.969 to 10.404 between pair-wise populations and was 3.504 among all of the populations. The Jaccard similarity coefficient between individuals ranged from 0.26 to 0.88. The UPGMA dendrogram clustered all 67 accessions into 6 groups. In some cases accessions from same region were grouped together but in most cases, there was gene exchange. To study the genetic relationships among populations, a principal coordinate analysis (PCoA) based on Nei's genetic distances was performed. Results of this study showed that AFLP marker can be a useful tool for investigating the genetic diversity of pomegranate genotypes.     

Genetic survey of 10 Indian coconut landraces by simple sequence repeats (SSRs)

A rich genetic diversity of coconut exists in farmer's fields, which represent valuable genetic resource for breeding. The study was conducted to assess the pattern of diversity in 102 coconut palms representing 10 landraces from 3 coconut-growing communities of India using 14 simple sequence repeat (SSR) markers. A total of 90 alleles were detected with an average of 6.42 alleles per locus and an average polymorphism information content of 0.61. Expected heterozygosity (H_e) was highest for the two tall landraces from Pallikkara community, while the least heterozygosity was observed for the dwarf coconut landraces from Vayalar community. Mean fixation index (F_ST) of 0.42 indicates a high level of population differentiation. A low gene flow (N_m) of 0.37 was observed. Based on molecular data, genetic similarities were calculated. The unweighted pair group method with arithmetic averages (UPGMA) cluster analysis grouped the landraces according to their geographical locations and breeding behaviour. The practical implications of this study in farmer participatory evaluation and conservation of coconut genetic resources are highlighted.     

Use of ISSR,SRAP, and RAPD markers to assess genetic diversity in Turkish melons

The genetic relationships among 63 melon (Cucumis melo L.) genotypes collected from various regions of Turkey were determined by comparing their molecular ISSR, SRAP, and RAPD markers with those of 19 foreign melon genotypes to investigate the taxonomic relationships and genetic variation of Turkish melon germplasm. Total 162 polymorphic markers (69, 18, and 75 obtained from ISSR, SRAP, and RAPD primers, respectively) were used to define the genetic similarity among the melon genotypes by dendrogram or two and three dimensional scalings. The average similarity (SM coefficient) between any two pairs of accessions examined as estimated by molecular variation was 0.73 ± 0.48. Within-group genetic similarities ranged between 0.46 and 0.96. Related genotypes or genotypes collected from similar regions were partitioned to similar clusters. Southeastern Anatolian genotypes were distinctly apart from group inodorus and group cantalupensis (sweet) genotypes. This reinforced the position of Turkey in the secondary genetic diversity center of melon. The genetic diversity among Turkish genotypes (H = 0.28 and I = 0.42) was only a little less than that of the world accessions (H = 0.30 and I = 0.45). On the other hand, the percentage of polymorphic loci among Turkish melon genotypes (90.7%) was even higher than that of the world accessions (87.6%).     

Newly developed SSR markers reveal genetic diversity and geographical clustering in Paeonia suffruticosa based on flower colour

Tree peony (Paeonia suffruticosa Andr.), considered by many to be the national flower of China, is famous for its ornamental, medicinal and culinary attributes. In this study, a total of 8,663 Simple Sequence Repeats (SSRs) were detected by means of a microsatellite search of unigene sequences identified from the de novo assembly of sequence data from different genotypes of tree peony from the Zhongyuan group. Among 100 randomly selected SSR markers, 25 were successfully amplified and showed polymorphism in 31 tree peony accessions. The number of polymorphic alleles ranged from 3 to 11 for each locus and the polymorphism information content value (PIC) ranged from 0.58 to 0.85, with a mean of 0.73, indicating a high level of discriminative capability. To analyse the genetic diversity, a phylogenetic tree was constructed, which demonstrated that tree peonies of similar flower colour were clustered together. The large number of tree peony SSR markers identified in this study will be valuable in studies in genetic diversity and linkage map construction, in gene localisation and cloning and in molecular-marker-assisted breeding in tree peony.     

Analysis of genetic diversity in Portuguese Ceratonia siliqua L. cultivars using RAPD and AFLP markers

Although carob (Ceratonia siliqua L.) is of great economic importance little is still known about the pattern of genetic variation within this species. Morphological characteristics based on 31 fruit and seeds of continuous characters determinant for agro-industrial uses, were compared with RAPD and AFLP markers for assessing genetic distances in 68 accessions of carob trees, from different cultivars, varieties and eco-geographic regions of Algarve. Eighteen selected RAPD primers applied to the 68 accessions produced a total of 235 fragments ranging from 200 to 2000 bp, of which 93 (40%) were polymorphic. Four AFLP selective primer combinations generated a total of 346 amplification fragments of which 110 were polymorphic. The average level of polymorphism based on four primer combinations was 31.8%. The phenetic trees based on RAPD and AFLP analyses gave high co-phenetic correlation values, and were found to be consistent in general with the analysis of morphological data, carried out on the same accessions. A number of RAPD and AFLP markers were found to be diagnostic for ‘Canela’ cultivar and 13 wild ungrafted trees.     

Water-use efficiency and evapotranspiration of mango orchard grown in northeastern region of Brazil

Knowledge of evapotranspiration (ET) and water-use efficiency (WUE) is essential in crops management mainly in arid and semiarid regions where water resources are scarce for irrigation. Field experiments were conducted at a commercial farm to obtain the WUE and ET of mango orchard growth in a semiarid environment of northeastern region of Brazil. Measurements were performed within a randomly selected experimental plot with the spacing of 10 m × 5 m between rows and plants. Soil water balance method was used to obtain the mango orchard evapotranspiration while the Penman–Monteith method (FAO/56) was used for determination reference evapotranspiration (ET_o). Soil water content was determined by six tensiometer sets installed at 0.20 m layer intervals from the soil surface down to 1.20 m soil depth. The experimental plot was irrigated with a sprinkler irrigation system based on four irrigation levels (T1 = 70%, T2 = 80%, T3 = 90% and T4 = 100% of ET_o. Results showed that ET and WUE are strongly influenced by soil water availability. Mango yield varied from a minimum value of 28.06 ton/ha in treatment T4 to a maximum value of 31.06 ton/ha in treatment T3. Such difference was found to be statistically significant (P < 0.05) by Tukey's test. Results also indicated that WUE values based on irrigation and evapotranspiration were maximum and minimum for low (treatment T1) and high (treatment T4) water levels, respectively.     

Fingerprinting of three typical macrosperma Italian lentil (Lens culinaris Medik.) landraces using fluorescence-based AFLP markers

Italian lentil landraces are principally cultivated for self or local consumption. Most of them are disappearing, particularly macrosperma types by being less required by the market. A pre-requisite for the conservation and the efficient use of genetic resources is the better understanding of the extent and the distribution of the existing genetic variation, useful for future breeding programmes. Our study was undertaken to analyse and quantify the genetic diversity within and among three macrosperma Italian lentil landraces (Onano, Altamura and Villalba), using fluorescent AFLP markers. AFLP markers generated information to differentiate among closely related genotypes and group within the same cluster individuals belonging to the same landrace. The total genetic diversity (H_T), the genetic diversity within population (H_S) and the extent of differentiation between populations (D_ST) were 0.198, 0.155 and 0.043, respectively. The fixation index (G_ST = 0.219) showed that about 78% of the observed total genetic variation can be attributed to within population differences and around 22% is due to differences among populations. The gene flow estimate (N_m = 1.774) and the mean genetic distance value (0.077) suggested narrow genetic base among the analysed populations, confirming the tendency of Italian lentil landraces to group together. The present study showed that fluorescence-based AFLP technique is a biotechnological tool that can provide significant insights for research in genetic diversity of lentil landraces and their subsequent conservation and utilization in breeding programs.     

Origin and genetic diversity of Tunisian grapes as revealed by microsatellite markers

Ten SSR loci, previously developed for grapevine, were analyzed to evaluate the genetic variability, cultivar relatedness, and parentage in a collection of 61 autochthonous Vitis vinifera cultivars from Tunisia.The number of alleles per locus ranged from 6 to 11, while the number of genotype patterns varied between 10 and 21. The expected heterozygosity varied between 0.621 and 0.855 and the observed heterozygosity was higher than 0.9 at 4 loci (VVMD28, VVMD5, VVIP31 and VVS2) indicating that the SSRs were highly informative.Cluster analysis using unweighted pair group method with arithmetic averaging (UPGMA) suggested 14 groups among studied cultivars and 53 grapevine denominations out of 61 were unequivocally distinguished, with all accessions showing at least one-specific combination of alleles.On the other hand, in order to overcome the existing confusion in Tunisian grapevine nomenclature, of the analyzed homonymous pairs of cultivars, only ‘Balta 2’ and ‘Balta 3’ have shown identical allelic profiles, consistent with their being the same genotype. Hence, nomenclature distinction is meaningless and only one denomination should be retained.Due to the high overall power of exclusion (Q) (greater than 99.99%) and to the absence of null alleles, the set of microsatellite loci used is appropriate to determine parentage in Tunisian grapevines beyond any reasonable doubt. The analysis of fingerprints indicated that the Tunisian grape vines have evolved through out crossing between five possible parents: Balta 1, Beldi Baddar, Beldi Rafraf, Beldi Local Rafraf and Khedhiri 3.     

Diversity,relationships, and genetic fingerprinting of the Listada de Gandía eggplant landrace using genomic SSRs and EST-SSRs

Listada de Gandía is one of the most renowned Spanish eggplant (Solanum melongena L.) landraces. Assessing its genetic diversity and relationships, as well as devising tools for its identification, is of great relevance for the enhancement and protection of this landrace. Forty-two eggplant accessions, which included 25 Striped accessions, of which 19 were of the Listada type (six accessions of Listada de Gandía, eight of Other Spanish Listada, and five of Non-Spanish Listada) and six of the Other Non-Spanish Striped group, and 17 Non-Striped accessions were characterized with 17 genomic SSRs and 32 EST-SSRs. Genomic SSRs had, as a mean, a greater polymorphism and polymorphic information content (PIC) than EST-SSRs. Although Listada de Gandía proved to be genetically diverse, specific and universal alleles for two SSR markers were found for this landrace. All the Listada accessions cluster together in the multivariate PCoA and UPGMA phenograms performed, and are separated from the Other Non-Spanish Striped and Non-Striped accessions. Also, Listada de Gandía accessions were clearly differentiated from the Other Spanish Listada and Non-Spanish Listada accessions in these analyses. SSR markers revealed of great utility to obtain a specific fingerprint for the Listada de Gandía eggplant as well as to establish the uniqueness and distinctness of this landrace. This information will be very helpful for the enhancement and protection from imitation of Listada de Gandía, and contributes to support its potential recognition with a Protected Designation of Origin (PDO) status.     

Isozyme polymorphism in Curcuma alismatifolia Gagnep. (Zingiberaceae) populations from Thailand

Over-collection of Curcuma alismatifolia Gagnep. and habitat destruction had greatly reduced the number of individuals in their natural habitat resulting in genetic erosion. We conducted the isozyme analyses to reveal the genetic diversity among natural populations compared with the cultivated populations. Out of seven enzyme systems analyzed in this study, five enzymes (ADH, GDH-1, LAP-1, GPI-2, PGM) which gave reproducible and consistent bands were used; DIA and EST were excluded due to their complex and inconsistent bands. The GPI-2 loci showed the most variable with six allozymes and 10 zymogram patterns followed by GDH-1 with 5 and 5, ADH with 3 and 5, PGM with 4 and 4, and LAP-1 with three allozymes and four zymogram patterns. Cultivated populations from Japan (cJ) and Thailand (cT) had the lowest percentage of polymorphic loci (P=40–60%), alleles per locus (A_l=1.8), alleles per polymorphic locus (A_p=2.33–3.00), and gene diversity (H_s=0.216–0.304) compared with two lowland populations (L1, L2) with P=100%, A_l=3.0–3.2, A_p=3.0–3.2, H_s=0.465–0.496; and six highland populations (H1–H6) with P=80–100%, A_l=2.4–3.8, A_p=2.4–3.8, H_s=0.342–0.659. Within population, H1 (the highest elevation sampled in this study) had the greatest genetic diversity (H_s=0.659). Mean genetic diversity over all loci across all populations was 0.444. Mean genetic identity between cultivated populations (I_C), lowland populations (I_L), among highland populations (I_H), and across all populations (I_SP) were 0.950, 0.947, 0.944, and 0.922, respectively. Using UPGMA cluster analysis, H1 and cJ were separated first from the rest into distinct groups. Two lowland populations were placed together with H6, while cT was grouped in the same cluster of H2–H5.     

Discrimination of ‘San Marzano’ accessions: A comparison of minisatellite, CAPS and SSR markers in relation to morphological traits

‘San Marzano’ (SM) is one of the most widely known tomato (Solanum lycopersicum L.) cultivars, and is a classic example of a local variety with a premium value. Unfortunately, the original cultivated form is underrepresented in the Protected Denomination of Origin (PDO) area because of the incidence of contaminant and phenotypically similar genotypes. Our aim was to examine the ability of three DNA marker systems (minisatellite, cleaved amplified polymorphic sequence (CAPS) and simple sequence repeat (SSR)) to reveal the genetic diversity of tomato accessions that were, based on a morphological analysis, very similar. The data indicate that both minisatellites and SSRs can be used to genetically distinguish the analysed materials. Furthermore, these two marker systems depict relationships consistent with the hierarchal pattern obtained by the morphological data. As locally cultivated tomato accessions are often characterised by some degree of genetic variability, our results will be valuable in facilitating the purification, management and breeding of tomato germplasms. The differences between the marker systems employed are also discussed in relation to their usefulness in the agro-food chain.     

Capability of the ‘Ball-Berry’ model for predicting stomatal conductance and water use efficiency of potato leaves under different irrigation regimes

The capability of the ‘Ball-Berry’ model (BB-model) in predicting stomatal conductance (g_s) and water use efficiency (WUE) of potato (Solanum tuberosum L.) leaves under different irrigation regimes was tested using data from two independent pot experiments in 2004 and 2007. Data obtained from 2004 was used for model parameterization, where measurements of midday leaf gas exchange of potted potatoes were done during progressive soil drying for 2 weeks at tuber initiation and earlier bulking stages. The measured photosynthetic rate (A_n) was used as an input for the model. To account for the effects of soil water deficits on g_s, a simple equation modifying the slope (m) based on the mean soil water potential (Ψ_s) in the soil columns was incorporated into the original BB-model. Compared with the original BB-model, the modified BB-model showed better predictability for both g_s and WUE of potato leaves on the parameterization data set. The models were then tested using the data from 2007 where plants were subjected to four irrigation regimes: non-irrigation (NI), full irrigation (FI), partial root-zone drying (PRD), and deficit irrigation (DI) for 3 weeks during tuber initiation and earlier bulking stages. The simulation results showed that the modified BB-model better simulated g_s for the NI and DI treatments than the original BB-model, whilst the two models performed equally well for predicting g_s of the FI and PRD treatments. Although both models had poor predictability for WUE (0.47 < r² < 0.71) of potato leaves, the modified BB-model was able to distinguish the effects of the irrigation regimes on WUE being that the WUE was generally greater for PRD than for FI and DI plants. Conclusively, the modified BB-model is capable of predicting g_s and of accounting for the differential effects of irrigation regimes on WUE of potato leaves. This information is valuable for further simulating potato water use thereby optimizing WUE under field conditions.