Drought tolerance variability in S<Subscript>1</Subscript> pollinator lines developed from a sugar beet open population

Drought tolerance is one of the most important objectives of sugar beet breeding programs in semi-arid regions, particularly during the last decade. Due to global climate changes and limitations of agricultural irrigation water, varieties with drought tolerance are taken into consideration in order to avoid yield losses due to drought. In this study, drought tolerance of 76 S₁ lines (full-sib families) that had been extracted from a genetically broad base multigerm sugar beet open pollinated population, were examined. Test crosses were made between the lines as pollinators and a cytoplasmic male sterile (CMS) single cross. The consequent hybrids along with checks were evaluated during 2007 and 23 more tolerant hybrids during 2008, in two adjacent experiments under drought stress and non-stress conditions. Drought tolerance indices calculated based on sugar yield, such as mean productivity (MP), geometric mean productivity (GMP) and stress tolerance index (STI) were used to assess hybrids responses to drought. The results showed significant genetic differences for root yield and sugar yield under both conditions. Drought tolerance indices displayed significant genetic variability for sugar yield among the hybrids. Many hybrids were drought tolerant as compared with the original base population as indicated by their high STI. The estimates of heritability for sugar yield in stress and non-stress conditions were much close to each other (0.31 and 0.34, respectively). Whereas, for root yield the heritability estimate in stress condition (0.46) was relatively higher than that in non-stress condition (0.34). Significant differences were observed among the selected hybrids for root yield and sugar yield, indicating genotypic variability for pollinator lines derived from the population. There were no significant differences for sugar content. For increasing the drought tolerance potential in a breeding population and developing drought-tolerant varieties by male parent, the drought-tolerant lines could be used.     

Analysis of QTL for yield-related traits in cassava using an F<Subscript>1</Subscript> population from non-inbred parents

A cassava F₁ population raised from the cross SC6 × Mianbao was used to construct a genetic linkage map. The map incorporated 200 polymorphic amplified fragment length polymorphism, sequence-related amplified polymorphism, simple sequence repeat (SSR), and expressed sequence tag (EST)–SSR markers which fit a 1:1 segregation ratio. It comprised 20 linkage groups (LGs) and spanned a genetic distance of 1645.1 cM with an average marker interval of 8.2 cM. Fifty-seven repeatedly detected QTLs (rd-QTLs) for three phenotypic traits (fresh root yield, root dry matter content, and root starch content) were identified in the F₁ population in four trials of year 2003, 2004, 2005, and 2008 by inclusive composite interval mapping. Among the 57 rd-QTLs, 25 rd-QTLs were linked to SSR/EST–SSR markers, which will help to facilitate marker-assisted selective breeding in cassava, and 15 marker intervals on ten LGs showed pleiotropic effects.     

Introgression of whitefly (<Emphasis Type="Italic">Aleurotrachelus socialis</Emphasis>) resistance gene from F<Subscript>1</Subscript> inter-specific hybrids into commercial cassava

The most widespread disease of economic importance of cassava is caused by whitefly vector, both as a single strain or combination of strains. A B₁P₂ family was generated from the crosses of an inter-specific F₁ hybrid (CW 198-11) as a female parent with a commercial cassava cultivar (MTAI-8) as male parent at CIAT headquarters and evaluated in a high-pressure zone for whiteflies in Colombia. 227 genotypes were scored using a scale ranging from 1 (no leaf damage) to 6 (considerable leaf necrosis and defoliation, sooty mould on mid and lower leaves and young stems). The rest were considered promising. The most promising resistance was for damage ratings below 2 for 17.8% of the genotypes. The availability of the pest resistance genotypes, will serve as a means to combat the problem of CMD in Africa provided that resistance to A. socialis is also effective against B. tabaci with different virus strains that is capable of been introduced.     

Analysis of hybrid lethality in F<Subscript>1</Subscript> wheat-rye hybrid embryos

The effect of the Embryo lethality mutant (Eml) of rye was studied in crosses between hexaploid wheat and corresponding inbred rye line (L2). Histological analysis of hybrid embryos revealed morphological differences 16 days after pollination. Eml was found to arrest the formation of shoot meristem but had no influence on root meristem formation. The effect of Eml cannot be overcome by in vitro embryo rescue via direct regeneration on Kruse medium. The possibility of complementary interactions between wheat and rye genes and of changes in gene expression through increased variation in dosage-regulated gene expression during hybrid formation is discussed.     

Ordering dominant markers in F<Subscript>2</Subscript> populations

Ordering dominant markers in F₂ populations is considered a difficult problem. The difficulties arise from the fact that recombinations cannot be observed directly from the data. In general, the multi-point maximum likelihood would be the appropriate criterion for ordering markers. This criterion takes into account all available information present in marker data. However, calculation of multi-point maximum likelihoods is very time-demanding, especially if the number of markers is large. In this paper, ordering markers by minimising the number of recombinations between adjacent markers is used as a simple alternative to multi-point maximum likelihood. Contrary to multi-point maximum likelihood, this method does not involve any probability assumptions about the occurrence of recombination events. Simulated data indicate that the minimum number of recombinations between adjacent markers is approximately a linear function of the map length obtained by multi-point maximum likelihood. As a consequence, it will lead to more or less the same optimum marker orders. Optimisation of marker orders with regard to the number of recombinations between adjacent markers is carried out by a modified form of simulated annealing. The reliability of the resulting marker orders is studied by generating marker orders that are plausible with the data using a Metropolis algorithm.     

Responses to selection of S<Subscript>5</Subscript> inbreds for broad-based resistance to ear rots and grain mycotoxin contamination caused by <Emphasis Type="Italic">Fusarium</Emphasis> spp. in maize

Random S₅ inbreds derived from three F₂ maize (Zea mays L.) populations (L1934 × LP918, LP915 × LP2541 and L7310 × L7266) were selected for ear rot resistance after inoculation with a low-fumonisin producing isolate belonging to F. proliferatum. The four less susceptible and the four most susceptible inbreds from each population were crossed and F₁ seeds were pooled. Resistant and susceptible pools from each population were evaluated for disease severity (percentage of the ear visibly diseased) after inoculation with the isolate used for selection, and high toxigenic isolates belonging to F. verticillioides and F. graminearum. Grain mycotoxin concentration was assessed by ELISA. Differences in disease resistance to each fungus were observed between resistant and susceptible pools in most populations and environments indicating that selection after inoculation with a single species might be effective to develop broad-based resistance to Fusarium. Resistant pools exhibited, after inoculation with F. verticillioides, low grain fumonisin concentrations in most populations and years. Positive genotypic correlations between disease severity and fumonisin concentration (0.89 < r_g < 0.98, depending on fungal species and year) indicate that selection for disease severity accounted for most of the variability for field fumonisin accumulation. Selection seemed to be also effective to reduce grain deoxynivalenol and zearalenone concentrations after inoculation with F. graminearum. Ratios between grain deoxynivalenol concentration and disease severity were lower in L7310 × L7266 than those observed in the other populations suggesting that mechanisms affecting mycotoxin accumulation might exist in this population and additional responses should be feasible if including deoxynivalenol concentration as another selection parameter.     

Effect of temperature on gametophytic selection in a <Emphasis Type="Italic">Phalaenopsis</Emphasis> F<Subscript>1</Subscript> population

Gametophytic selection has potential to increase the efficiency of breeding for temperature tolerance. Here, we describe orchid seedlings after application of low and high temperatures during gametophytic development. In addition to phenotypic traits, amplified fragment length polymorphism (AFLP) markers were used to determine the genetic variability in seedlings. Two hybrid Phalaenopsis were cross-pollinated and exposed to 30°C day/25°C night for 3 days for a warm pollination or 15°C day/10°C night for 7 days as a cold pollination treatment. The plants were returned to the greenhouse after pollination and green capsules were collected after 150 days. Protocorms obtained from these treatments were evaluated 72 days after initial plating for germination and size on a thermogradient table ranging from 10 to 30°C. Seedlings were then evaluated 1 year after initial plating. The mean number of roots per seedling (4.2) was greater for plantlets that derived from the cold pollination treatment compared to those from warm pollination (3.6). Weight of the seedlings, number of roots and the average root length were significantly affected by the interaction between pollination treatment and germination temperature. The weight, number of leaves, and average root length were significantly affected by the interaction between pollination treatment and incubator/growth chamber. The results indicated that seedlings derived from warm pollination were more vigorous under warm growing conditions and those derived from cold pollination were more vigorous under cold growing conditions. Genetic variation among 16 F₁ seedlings randomly selected from various temperature treatments was analyzed. A dendrogram based on 651 loci resulted in three major groups and one subgroup. The groups and subgroup revealed common selection pressure during the gametophytic stage. The AFLP data support genetic differentiation of Phalaenopsis hybrids pollinated under different temperatures.     

Estimation of genetic distance and its predictability of F<Subscript>1</Subscript> hybrid performance in barley

Heterotic performance of hybrids is dependent upon the amount of genetic variability among parents and combining ability of alleles at the loci associated with target traits. This study was carried out to determine if (1) pedigree-based genetic distance could explain molecular levels of genetic diversity, and (2) molecular marker-based genetic distance could predict the degree of hybrid performance in barley. The average value of Random Amplified Polymorphic DNA (RAPD)-based genetic similarity for all 58 genotypes was 0.641. Twenty-two hulless barley and eight malt barley varieties showed low levels of genetic diversity with higher similarity values than the average of all or of the hulled barley variety pool. Coefficients of parentage (COPs) computed for 1,653 pairs of 58 Korean barley varieties ranged from 0 to 0.984 with a mean of 0.048. Correlation between the genealogical and RAPD-based genetic similarity matrices was 0.256 (P < 0.01). Correlation values for the related and for all (related + unrelated) genotype pairs were almost similar to each other, indicating that the unrelated genotypes share a large portion of genomes alike in state, not identical by descent. RAPD-based genetic similarity estimates among parents were poorly correlated with their hybrid performance such as 1,000-grain weight (r = 0.34), biomass yield (r = −0.12), and grain yield (r = −0.04) for 11 genotype pairs of hulled barley. However, correlations between heterozygosity at marker loci and hybrid performance for biomass and grain yield slightly increased when two F1 hybrids were excluded in the analysis due to their low yield.     

Genetic combining ability estimates in the F<Subscript>1</Subscript> and F<Subscript>2</Subscript> generations for yield,its component traits and alkaloid content in opium poppy (<Emphasis Type="Italic">Papaver somniferum</Emphasis> L.)

The F ₁ and F ₂ generations of a twenty parent fractional diallel cross of opium poppy (P. somniferum L.) were analyzed for combining ability for ten quantitative and five quality (alkaloids) traits. The results indicated significant differences among the parents for combining ability for all the traits. The GCA and SCA components of variances were significant for all the characters. However, the SCA component of variance (δ ²s) was predominant indicating the preponderance of non-additive gene effect for all the traits except for leaves/plant and papaverine in F₁ hybrids. The average degree of dominance (δ ²s/δ ²g) was more than unity indicating over dominance and also confirming non-additive mode of gene action. Among the parents IS-16, IS-13 and NBRI-1 for early flowering, BR226 and BR241 for branches/plant, capsule weight/plant, seed yield/plant and husk yield/plant, BR227 for leaves/plant, UO1285 for capsule size and opium yield/plant, NBRI-5 for husk yield/plant, morphine, codeine, and thebaine and ‘Papline’ for plant height and papaverine content were found good general combiners. Parent ND1001 was good combiner for codeine and narcotine content. Inclusion of good general combiners in a multiple crossing program or an intermating population involving all the possible crosses among them subjected to bi-parental mating may be expected to offer maximum promise in breeding for higher opium, seed yield and alkaloid contents.     

Genetic variation in F<Subscript>2</Subscript> populations and their potential in the improvement of grain yield in tef (<Emphasis Type="Italic">Eragrostis tef</Emphasis>)

Tef is a staple cereal of Ethiopia in high demand by consumers. In order to cope up with this high consumer demand, productivity per unit of land must increase through the development and use of high-yielding varieties. To this effect, the National Tef Research Project has long been striving towards the development of high yielding varieties through direct selection from germplasm and concentrating favourable alleles through hybridization and selection, despite the tedious crossing technique. The objective of this study was to assess the degree of genetic variation in F₂ populations of tef as a basis for improving grain yield. F₂ populations from 12 crosses and their parents were grown at the Debre Zeit Agricultural Research Center, Ethiopia, and assessment was made on eight traits on individual plant basis. Eleven of the 12 crosses showed substantial genetic variation for grain yield and its components, indicating the potential for improvement through selection. Moreover, grain yield, plant weight and yield related traits showed moderate to high heritability values (17–80%). In all the crosses, tiller number, panicle weight, yield per panicle and panicle length showed significant (P ≤ 0.05) and positive association with grain yield. Considering the degree of genetic variation and heritability values, emphasis should be given to selected crosses in an effort to developing high-yielding tef varieties.     

QTL detection for grain oil and starch content and their associations in two connected F<Subscript>2:3</Subscript> populations in high-oil maize

High-oil maize (Zea mays L.) has special value in animal feed and human food. Two hundred and eight-four and 265 F_2:3 families developed from two crosses between one high-oil maize inbred and two normal dent maize inbreds were evaluated for grain oil and starch contents under two environments. Using composite interval mapping, 1–6 QTL for each trait were detected under each environment and in combined analysis in both populations. Only one common QTL across two environments in each population and across two populations were found for starch content. Among the detected QTL, nine digenic interactions with small effects were identified. Comparison of single-trait QTL and the results of multiple-trait QTL mapping showed that oil content might be complicatedly correlated with starch content. Although single-trait QTL with the same parental effects for both traits and oil-starch QTL were all detected at the same genetic bin 6.04 as the cloned high-oil QTL (qHO6) with no unfavorable effects on grain weight, our results did reflect the difficulty to realize simultaneous improvement on grain oil and starch contents. Of course, these results should be validated in further experiments under more environments using RILs, NILs and other permanent populations.     

Individual reaction of <Emphasis Type="Italic">Capsicum</Emphasis> F<Subscript>2</Subscript> hybrid genotypes in anther cultures

The present study evaluated the individual plants reaction of F₂ hybrid generation of C. annuum: ATZ1 × PO and ATZ1 × CDT as well as two interspecific hybrids: C. frutescens × C. annuum ATM1 and C. frutescens × C. chinense on androgenesis conditions in in vitro anther cultures. The experiment was carried out following a modified method of Dumas de Vaulx et al. (Agronomie 1:859–864, 1981). There were demonstrated clear differences in the effectiveness of androgenesis both between the pepper hybrid forms as well as among individual plants of all the genotypes tested. The highest effectiveness of androgenic embryos development was observed for the cultivated form of C. annuum: (ATZ1 × PO)F₂. Anthers of most of the plants of this hybrid produced embryos at the level higher than 5%, while in anther cultures of the second C. annuum hybrid (ATZ1 × CDT)F₂ almost 3-fold fewer embryos and plants were produced. Anthers isolated from flower buds of interspecific hybrids formed much lower number of embryos. A positive reaction was recorded for five hybrid plants of (C. frutescens × C. annuum ATM1)F₂, while in case of (C. frutescens × C. chinense)F₂ androgenic embryos were obtained from anthers of two plants. Only in the case of a one of these plants did the effectiveness of androgenesis exceed 5%. The ploidy level of the regenerants was determined by flow cytometry. Among the regenerants there were observed both haploid forms and the plants with the diploid number of chromosomes.     

Genetic analysis reveals a dominant <Emphasis Type="Italic">S</Emphasis> locus and an <Emphasis Type="Italic">S</Emphasis> suppressor locus in natural self-compatible <Emphasis Type="Italic">Brassica napus</Emphasis>

A self-incompatible (SI) line, S-1300, and its maintainer 97-wen135, a self-compatible (SC) line, were used to study the inheritance of maintenance for self-incompatibility in B. napus. The ratio of SI plants to SC plants from S-1300 × 97-wen135 F₂ and (S-1300 × 97-wen135) × 97-wen135 was 346:260 and 249:232, fitting the expected ratio of 9:7 and 1:1, respectively. Based on these observations, here we propose a genetic model in which two independent loci, S locus and S suppressor locus (sp), are predicted to control the inheritance of maintenance for self-incompatibility in B. napus. The genotypes of S-1300 and 97-wen135 are S ₁₃₀₀ S ₁₃₀₀ sp ₁₃₀₀ sp ₁₃₀₀ and S ₁₃₅ S ₁₃₅ sp ₁₃₅ sp ₁₃₅ , respectively. S ₁₃₅ is dominant to S ₁₃₀₀ , but coexistence of sp ₁₃₀₀ and sp ₁₃₅ fails to suppress S locus. Both S ₁₃₀₀ and S ₁₃₅ can be suppressed by sp ₁₃₅ , while sp ₁₃₀₀ can suppress S ₁₃₅ but not S ₁₃₀₀ . The model contains two characteristics: that a dominant S locus exists in self-compatible B. napus, and that co-suppression will occur when sp loci are heterozygous. The model has been validated by the segregation of S phenotypes in the (S-1300 × 97-wen135) × S-1300, the progenies of SC S-1300 × 97-wen135 F₂ plants and DH population developed from S-1300 × 97-wen135 F₁. This is the first study to report co-suppression of S suppressor loci in B. napus. The genetic model will be very useful for developing molecular markers linked to maintenance for self-incompatibility and for dissecting the mechanism of SI/SC in B. napus.     

Development of CGMS system in ridge gourd [<Emphasis Type="Italic">Luffa acutangula</Emphasis> (Roxb.) L.] for production of F<Subscript>1</Subscript> hybrids

Cytoplasmic male sterile system in ridge gourd has been converted to cytoplasmic genetic male sterile (CGMS) system through the development of analogues of male sterile (MS) line, maintainer line and fertility restorer line. These lines were developed by crossing the MS mutant, regenerated through in vitro culture, with monoecious pollen parents Deepthi, Haritham, LA 101, CO 2, IC 92761 and IC 92685. All hybrids and the BC₁ generation developed by crossing with the recurring pollen parents Deepthi, Haritham and LA 101 were male sterile. Male sterile BC₁ plants have been advanced to BC₆ generation and the parental line LA 101 was proved to be a successful maintainer line, producing male sterile progeny in successive back cross generations. Analogue of cytoplasmic male sterile line, MS LA 101, was developed through back crossing and on crossing with fertility restorer lines Arka Sumeet and LA 102, this line excelled as female parent, resulting heterotic combinations. Mitochondrial marker rpS14 and SCAR Tm-53 were identified to yield male sterility specific markers whereas SSR marker 18956 has generated the male fertility specific marker. These primers are recommended for marker assisted selection of ridge gourd, for utilizing male sterility for hybrid seed production and for developing A, B and C lines in CGMS system.     

Selection for <Emphasis Type="Italic">Phytophthora</Emphasis> field resistance in the F<Subscript>2</Subscript> generation of organic outdoor tomatoes

Tomatoes are the most important vegetable, globally as well as in Germany. Outdoor tomato production is seriously impaired due to increasing infections with evolving late blight (Phytophthora infestans) populations. Within organic agriculture, research is being conducted to develop regionally adapted and open pollinated cultivars of outdoor tomatoes with late blight field resistance. In the present experiment, three crosses, including wild, cocktail, and beefsteak tomatoes, were selected for field resistance against late blight in F₂ at one location per cross. The comparison of positive and negative selection in F₃ revealed the selection of single F₂ plants to be efficient in all three crosses. F₂ selection has proved to be a robust and efficient tool for breeding programs. The correlated response to selection in other traits, including yield, fruit weight, days to maturity, harvest period, and plant height, depended on the cross. It was evident that selection for desired traits combined with field resistance against late blight is promising, even in wide crosses. The most undesired attribute of wild tomatoes is the formation of shoots on leaves and in inflorescences. No correlation was observed between field resistance and shoot formation, allowing the selection of genotypes with improved field resistance and yield, but without morphological disadvantages.     

Development of late-bolting F<Subscript>1</Subscript> hybrids of Chinese cabbage (<Emphasis Type="Italic">Brassica rapa</Emphasis> L.) allowing early spring cultivation without heating

We developed new F₁ hybrids of Chinese cabbage (Brassica rapa L. ssp. pekinensis) that allow cultivation earlier in spring without heating by introducing extremely late-bolting alleles at two homologs of the flowering repressor Flowering Locus C (BrFLC2 and BrFLC3) from non-heading ‘Leafy Green Parental Line No. 2’. These new F₁ hybrids were produced by the following four steps. First, the extremely late bolting selected lines were developed. These selected lines headed in spring after overwintering cultivation, whereas the conventional F₁ cultivars flowered. Secondly, an investigation of the three plantings showed that our F₁ hybrids formed heads when seeds were sown from mid-February to early March, whereas the conventional F₁ cultivar did not form heads because of premature bolting. Thirdly, we identified some F₁ hybrids with extremely late bolting during early spring cultivation in an investigation of many F₁ hybrids. Finally, based on an investigation across four cold regions for 2 years, we compared the commercialization rate, defined as the proportion of plants greater than 2000 g in weight and with a flowering stalk less than 10 cm long. Then we identified a F₁ of MS02 × 12-04 which had a high commercialization rate on average (92%), whereas the rates of three conventional F₁ cultivars were only 0–2%. In the near future, these F₁ hybrids will be valuable late-bolting cultivars despite climate change, permitting stable cultivation and harvest over wide regions.     

Fine mapping of the <Emphasis Type="Italic">R</Emphasis><Subscript><Emphasis Type="Italic">SC14Q</Emphasis></Subscript> locus for resistance to soybean mosaic virus in soybean

In maize hybrid seed production, some hybrid seed in the field must be harvested before reaching physiological maturity because of the potential damage from early fall frosts. However, early harvesting can result in poor quality and low vigor of seeds. To elucidate the genetic basis of seed vigor at different stages of maturity, the seeds of a set of recombinant inbred line (RIL) populations at three different stages of maturity (32, 40, and 45 days after pollination; DAP), were used to evaluate the performance of four traits for seed vigor in the field. A genetic linkage map was constructed using 217 SSR makers covering 2438.2 cM with an average interval of 11.2 cM. The results showed that there were significant positive relationships among the four traits of seed vigor at all three sampling times, and all showed quantitative changes according to the degree of maturity of the seeds. However, the four traits of seed vigor were not significantly related to the 100-kernel weight. In total, we detected 16 different QTL for the four measured traits of seed vigor at three sampling times; five QTL were for germination energy, three for germination percentage, four for germination index, and four for vigor index. Interestingly, four QTL for seed vigor, which were detected at all three sampling times, were located in the same region on chromosome 7. This result implies that this region of chromosome 7 is important for seed vigor of seeds harvested before they reach physiological maturity.     

Induction of 2n pollen formation in <Emphasis Type="Italic">Begonia</Emphasis> by trifluralin and N<Subscript>2</Subscript>O treatments

In this study, treatments of both trifluralin (at 10, 100 and 1000 μM) and N₂O (in the form of gas under pressure) were applied to Begonia flower buds to induce the formation of 2n pollen. Three male fertile species (B. cucullata, B. subvillosa var. leptotricha and B. fischeri) and two male sterile hybrids (B. schmidtiana × B. cucullata and B. subvillosa var. leptotricha × B. cucullata) were treated. Pollen size, which is related to pollen DNA content, increased after both N₂O and trifluralin treatments, but the induction of large pollen was genotype dependent. Trifluralin induced large pollen only in the male fertile species, while N₂O treatments induced fertile 2n pollen in the male sterile B. schmidtiana × B. cucullata. Cytological studies showed that trifluralin induced multinuclear monads that resulted in 4n gametes in stead of 2n gametes. In general, large pollen obtained after trifluralin treatments showed low germination capability, while large pollen obtained after N₂O treatments retained high germination capability. Seedlings with raised ploidy level could only be obtained after crosses were performed with large pollen obtained from N₂O treatments. Hence, N₂O treatments are preferable to the use of trifluralin to induce 2n gametes in Begonia.     

CO<Subscript>2</Subscript>-assimilation and chlorophyll fluorescence as indirect selection criteria for host tolerance against <Emphasis Type="Italic">Striga</Emphasis>

Striga hermonthica (Del.) Benth. is a parasitic weed on tropical cereals causing serious yield losses in Africa. The use of host crop varieties with improved resistance and tolerance against this parasite is a key component of an integrated control strategy. Breeding for tolerance is however seriously hampered by the absence of reliable and yet practical selection measures. The observation that the photosynthetic rate of tolerant genotypes is less sensitive to Striga infection was used as a starting point to search for suitable selection measures. In a greenhouse pot experiment the effect of Striga infection on the photosynthesis of four sorghum (Sorghum bicolor [L.] Moench) genotypes, differing in Striga tolerance level, was measured at three moments in time (26, 48 and 75 days after sowing). Genotypes were CK60-B, E36-1, Framida and Tiémarifing. Measurements involved CO₂-assimilation (A) and three chlorophyll fluorescence characteristics (electron transport rate through photosystem II [ETR], photochemical [Pq] and non-photochemical quenching [NPq]). Striga infection negatively affected A, ETR and Pq. Based on A and Pq, genotypes with superior levels of tolerance (Tiémarifing) could be discriminated from genotypes with superior level of resistance (Framida). Both A and Pq showed high heritabilities and consequently clear and predictable differences between genotypes. Using discriminative ability, heritability and cost effectiveness as main criteria, photochemical quenching (Pq) was concluded to possess the highest potential to serve as indirect selection measure for host plant tolerance to Striga. Screening should preferably be conducted at relatively high Striga infestation levels, between Striga emergence and host plant flowering.     

Description of a new trans-generic <Emphasis Type="Italic">S</Emphasis>kb-RNase allele in apple

Polish apple cvs: ‘Ligol’, ‘Odra’ and ‘Primula’ served for studies of self-incompatibility. Basing on available sequence data, a new set of primers upstream and downstream of the hypervariable (HV) region of apple S-RNases were designed. Using the RT-PCR method, cDNA was amplified on RNA isolated from styles. PCR products were cloned and sequenced. A new trans-generic S-RNase allele, designated as Skb (GenBank accession no. EU443101), was discovered in cvs ‘Odra’ and ‘Primula’. Nucleotide sequence alignment revealed that Skb-RNase shows 98% identity to SaucS19-RNase from Sorbus aucuparia and 97% identity to CmonS17-RNase from Crataegus monogyna. The occurrence of extensive intergeneric hybridization among extant Pyrinae is considered since the deduced amino acid sequence of Skb-RNase from M. × domestica showed higher similarity to CmonS17 from C. monogyna, SaucS19-RNase from S. aucuparia, St from Malus transitoria, S5-RNase and S3-RNase from Pyrus pyrifolia, and S40-RNase from P. ussuriensis than to S-alleles from Malus × domestica and all of them are grouped in the same cluster of phylogenetic tree. In respect to extremely high similarities between aforementioned S-RNases it could be possible that these alleles existed before the separation of Malus, Pyrus, Sorbus and Crataegus genera. Within Malus, the Skb-RNase from M. × domestica and St-RNase from M. transitoria show 100% identity of the HV region at the deduced amino acid level, suggesting that these S-RNases diverged more recently than the other Malus S-RNases. In ‘Ligol’, the agronomically most important cultivar in Poland, the S2 and S9 were identified.