Superior Vigor Research Articles

Enhanced Growth, Haematological and Biochemical Performance in Hybrid Catfish of Clarias gariepinus x Clarias cavernicola

This study evaluated the growth performance, haematological indices, and biochemical parameters of four catfish breeds, including two purebreds (Clarias cavernicola and Clarias gariepinus) and two hybrids (female C. cavernicola x male C. gariepinus and female C. gariepinus x male C. cavernicola). Over four months, growth was assessed by measuring body weight, total length, and standard length. Haematological and biochemical analyses were conducted to assess the health and immune status of the different breeds. The results indicated that the hybrid of female C. cavernicola x male C. gariepinus exhibited the highest growth performance, with significant increases in body weight and length compared to the other breeds. This hybrid also demonstrated the highest white blood cell (WBC) and lymphocyte counts, suggesting a stronger immune response, which was statistically significant (p<0.05) compared to the purebreds. Granulocyte levels were consistent across all breeds, while red blood cell (RBC) and platelet counts showed no significant differences, indicating stability in these parameters. Biochemical analysis revealed that the female C. cavernicola x male C. gariepinus hybrid had the highest total protein and globulin levels, which are indicative of better health and immune function. Albumin levels were higher in both hybrids compared to the purebreds, while cholesterol, creatinine, and glucose levels were similar across all breeds. The alleles associated with better immunity are likely present in the maternal line of C. cavernicola, leading to the superior vigour observed in the C. cavernicola (female) x C. gariepinus (male) hybrid. This enhanced vigour results in improved growth, hematological, and biochemical profiles. Compared to purebred breeds, this hybrid demonstrates better health, increased disease resistance, and a higher potential for productivity in aquaculture.

Creeping Bentgrass Nutritional, Morphological, and Putting Green Performance Response to Ca/Mg-Silicate Slag Liming Agent

While not classified as an essential plant nutrient, silicon (Si) assimilation following exogenous Si application has enhanced the wear resistance of cool-season turfgrass. Given this beneficial supplementation of lignin by Si reported in epidermal tissue of monocotyledonous plants, our research objective was to quantify root morphology, vegetative nutrition and vigor, soil chemistry, and putting green performance in response to split applications of pelletized liming agents rich in Si and/or Ca and Mg. Field evaluation of granular liming agent treatment, 2441 kg (ha year)−1, was conducted on creeping bentgrass (Agrostis stolonifera L. cv. Penn G-2) putting green maintained in the Mid-Atlantic US. Pelletized Ca/Mg-SiO3 slag or dolomitic limestone treatments were conducted in frequent split applications and incorporated into the upper 5 cm of the rootzone. Measurements of canopy color and density, shoot growth as clipping yield, soil pH, Si and nutrient content of clippings, and soil extractable Si were performed each season. Cumulative Ca/Mg-SiO3 application (kg ha−1) increased mean acetic acid (HOAc) extractable Si by 35 to 60 mg kg−1 and leaf Si content by 1.0 to 1.5 mg g−1. However, neither putting green canopy quality, shoot nutrient concentration, 5 to 15 cm depth root length density nor ball roll distance was improved by liming agent treatment. Liming agent-treated or untreated plots showed statistical, yet inconsistent, differences in clipping yield 4, 14, 15, 16, and 17 months from initiation (MFI). This thorough shuffling of treatment rank, resulting in identical experiment-wide means precludes the expectation of dependably superior vigor by any.

EVALUATION OF NEW BLUEBERRY CULTIVARS IN PEDOCLIMATIC CONDITIONS FROM RIFG PITESTI-MARACINENI

Vaccinum corymbosum is one of the species highly valued for the taste and dietary value of its berries. The new blueberry cultivars obtained in the breeding activity have high productivity, resistance to diseases and pests, and large and easily removable fruits. The success of the extension of blueberry crops depends on the adaptability of the cultivars to soil conditions and regional climate changes. A study was carried out at the Research Institute for Fruit Growing Pitesti-Maracineni, in the period 2019-2022, and was focused on the vegetative growth and fruiting processes, berries quality, and evaluated the disease and pest behavior of 13 new blueberry cultivars, currently in their 4th year ('Top Shelf', 'Blue Ribbon', 'Calypso' and 'Valor'), respectively 6 years from planting ('Duke', 'Bluejay', 'Draper', 'Liberty', 'Elliott' and 'Aurora'). The ripening period of the new cultivars covered a period between the second decade of June (12.06.2020, 'Duke') and the end of August (27.08.2021, 'Aurora', 'Last Call' and 'Elliott'). Depending on the age of fruit ripening, the cultivars were divided into very early ('Duke'), early ('Huron'), early-middle ('Blue Ribbon', 'Draper', 'Bluejay'), middle ('Top Shelf', 'Valor', 'Calypso'), late ('Cargo' and 'Liberty') and very late ('Last Call', 'Elliott' and 'Aurora'). At the end of the four years of study, the analysis of the data recorded for the vegetative growth and fruiting processes indicated that, for the younger plants (4th year after planting), for an average bush volume of 0.41m3 (0.14- 0.84 m3) berry yield fluctuated around 7.27 t/ha (1.66-16.59 t/ha). The cultivars with superior vigor were 'Valor', 'Last Call', and 'Cargo' (0.49-0.53 m3), the most productive being 'Cargo', with approximately 13.6 t /ha. For blueberry in the 6th year after planting, where the average volume of the bush was 0.53 m3 (0.19-0.82 m3), the fruit production was 6.89 t/ha (1.87 -14.4 t/ha). The cultivars with superior vigor were 'Bluejay', 'Aurora' and 'Liberty' (0.59-0.62 m3), and in terms of productivity, 'Duke' (9.13 t/ha) and 'Liberty' stood out (9.92 t/ha). For plants of the same age (3 and 4 years after planting), the average berry weight fluctuated around 2.25 g (0.7-5.72 g), the firmness recorded an average of 43.95 (15.9-77.50 units), while juice pH and total soluble substance content showed average values of 3.44 (2.24-5.72) and 13.32˚Brix (7.9-23.40). The highest berry weight was determined for 'Top Shelf' cultivar (2.9 g). The cultivars 'Aurora' and 'Last Call' stood out for their superior content of total soluble solids (17.14 and 16.01˚Brix), and the cultivars 'Blue Ribbon' and 'Top Shelf' for their high fruit pH (4.18 and 3.69). Last but not least, the high firmness of the fruits highlighted the Aurora and 'Blue Ribbon' cultivars (57.90 and 52.28 HPE-II-FFF Bareiss units). Regarding the phytosanitary status of the studied shrubs, increased sensitivity to diseases of the 'Huron' cultivar was highlighted (ISV 2.9%), especially to the attack of Phytophthora spp. (1.6%attack degree), which influenced significantly plant survival. At the end of the study period, we can recommend the cultivars 'Duke', Liberty', and 'Cargo' for cultivation in similar pedoclimatic conditions, the first standing out for its earliness and productivity, and the last two for their high fruit production.

Can we abandon phosphorus starter fertilizer in maize? Results from a diverse panel of elite and doubled haploid landrace lines of maize (Zea mays L.).

The importance of phosphorus (P) in agriculture contrasts with the negative environmental impact and the limited resources worldwide. Reducing P fertilizer application by utilizing more efficient genotypes is a promising way to address these issues. To approach this, a large panel of maize (Zea mays L.) comprising each 100 Flint and Dent elite lines and 199 doubled haploid lines from six landraces was assessed in multi-environment field trials with and without the application of P starter fertilizer. The treatment comparison showed that omitting the starter fertilizer can significantly affect traits in early plant development but had no effect on grain yield. Young maize plants provided with additional P showed an increased biomass, faster growth and superior vigor, which, however, was only the case under environmental conditions considered stressful for maize cultivation. Importantly, though the genotype-by-treatment interaction variance was comparably small, there is genotypic variation for this response that can be utilized in breeding. The comparison of elite and doubled haploid landrace lines revealed a superior agronomic performance of elite material but also potentially valuable variation for early traits in the landrace doubled haploid lines. In conclusion, our results illustrate that breeding for P efficient maize cultivars is possible towards a reduction of P fertilizer in a more sustainable agriculture.

Divergência genética e qualidade fisiológica de sementes de linhagens de mamoneira anã

ABSTRACT The development of new castor bean genotypes with high grain yield and physiological seed quality is fundamental to the economic success of the crop. This study aimed to evaluate the agronomic performance and physiological quality of seeds of twelve castor bean lines, in order to determine superior genotypes. Plant height, insertion height and number of racemes, grain yield, oil content, germination percentage and vigor were evaluated. The dwarf castor bean lines H4, H5 and H11 were responsible for a grain yield above 1,400 kg ha-1 and are, therefore, promising for getting new hybrids. The indirect selection of dwarf castor bean lines can be performed through morphologic traits. The lines H4, H6, H9, H11 and H12 produced seeds with superior vigor and germinative quality.

Heteromorphic seed germination and seedling emergence in the legume Teramnus labialis (L.f.) Spreng (Fabacaeae)

Seed heteromorphism can influence germination and ultimately seedling establishment, particularly in disturbed habitats. This study compared seed and seedling traits across three distinctly colored seed morphs (viz. light-brown, brown, and dark-brown) of the forage legume, Teramnus labialis (L.f.) Spreng. The best quality seeds (i.e., un-parasitized, filled and un-cracked) were brown: 389.3 quality seeds per 1000 units compared with <270/1000 units for the other two morphs. Length, width, volume, and water content were lowest in the light-brown and highest in the dark-brown seeds. Seed thickness and mass were lower in the light-brown seeds. Dark-brown seeds imbibed fastest from 2 h onwards. Germination was comparable across the morphs after 7 days but was lowest in the light-brown (17% at 21 days) and highest in the dark-brown seeds (36% at 21 days) at 14 and 21 days. At 7 days, seedling emergence in the dark-brown seeds (15.0%) was higher than in the other two morphs (4%–6%); this remained so at 14 and 21 days. Seedling growth (number of leaves, stem height and diameter, and root length) was superior in the dark-brown seeds. Seed heteromorphism in T. labialis may allow its persistence in disturbed habitats, and the dark-brown seeds are best suited for seeding in revegetation projects, given their superior germination capacity and seedling vigor.

Grafting Crop Shoots on Bi-clonal Seedlings as a Potential Strategy for Clonal Multiplication in Tea

Tea is chiefly propagated by means of cuttings consisting of a leaf and an internode prepared from the aperiodic shoots of pruned bushes. However, multiplication of the newly released potential tea clones by propagation of cuttings is constrained by an inadequate number of mother bushes and time requisite for pruning recovery. Therefore, to address this constraint two experiments were conducted to evaluate the suitability of crop shoots as scion material with appropriate controls. First, crop shoots of the clone TRF-2 were grafted on rooted seedlings of BSS-1, BSS-2, and BSS-3. Next, crop shoots of the clone TRF-4 were grafted on non-rooted rootstocks of the clones UPASI-2, UPASI-6, UPASI-9, and UPASI-26. The results revealed that grafting crop shoots as scions on BSS seedlings and non-rooted fresh rootstocks produced composite plants with superior vigor. However, an enormous reduction in graft success rate was found when crop shoots were grafted on non-rooted rootstocks. Also, significant variations were observed in plant vigor, depending upon the rootstock–scion combination. The crop shoots of TRF-2 grafted on BSS-1 seedlings and the crop shoots of TRF-4 grafted on the fresh rootstocks of UPASI-9 and UPASI-2 produced composite plants with superior vigor.

Proteomics of Maize Root Development

Maize forms a complex root system with structurally and functionally diverse root types that are formed at different developmental stages to extract water and mineral nutrients from soil. In recent years proteomics has been intensively applied to identify proteins involved in shaping the three-dimensional architecture and regulating the function of the maize root system. With the help of developmental mutants, proteomic changes during the initiation and emergence of shoot-borne, lateral and seminal roots have been examined. Furthermore, root hairs were surveyed to understand the proteomic changes during the elongation of these single cell type structures. In addition, primary roots have been used to study developmental changes of the proteome but also to investigate the proteomes of distinct tissues such as the meristematic zone, the elongation zone as well as stele and cortex of the differentiation zone. Moreover, subcellular fractions of the primary root including cell walls, plasma membranes and secreted mucilage have been analyzed. Finally, the superior vigor of hybrid seedling roots compared to their parental inbred lines was studied on the proteome level. In summary, these studies provide novel insights into the complex proteomic interactions of the elaborate maize root system during development.

Cytological and Morphological Evaluation of Interspecific Hybrids between Trifolium repens and T. uniflorum

A significant constraint to the vegetative persistence of white clover (Trifolium repens L.) is summer moisture stress. A closely related species, T. uniflorum L., has a robust root system that could provide drought resistance. Hybridization of these two species leads to the generation of fertile hybrids. A study was conducted to generate F1 hybrids and first backcrosses (BC1) to white clover, and to evaluate the fertility, meiotic chromosome behavior, and plant morphology of these hybrids. Marker chromosome counts of the F1 and BC1 individuals confirmed hybridity. Meiotic configurations of five F1 and five BC1 plants indicated close homology between the two species and homoeologous pairing of white clover subgenomes. To evaluate phenotypes, clones of 56 individual genotypes (seven F1, 32 BC1, and 17 elite white clover plants) were grown in sand. After 13 mo, the leaves, stolons, and roots were measured and the dry weights of shoots and roots were determined by destructive harvest. Pattern analysis of the genotype‐by‐trait data identified four progeny groups. The F1 progeny were confined to the group with the lowest mean expression for most root and shoot traits. Most of the BC1 progeny grouped with the elite white clovers, but two BC1 formed a group with superior vigor and morphology, combining the best root and shoot traits of both parents. These BC1 individuals with similar shoot morphology to white clover and a robust root system, similar to T. uniflorum, are being integrated into a program to breed drought‐resistant hybrids to replace white clover in dry environments.

Morphological and physiological traits of seeds and seedlings in two rice cultivars with contrasting early vigor

Early vigor is important for crop establishment in rice. This study was conducted to determine the seed and seedling traits in relation to early vigor in rice. Laboratory tests and pot experiments were carried out in 2013 and 2014. Morphological and physiological traits of seeds and seedlings were compared between two contrasting rice cultivars, Yuxiangyouzhan with superior early vigor and Huanghuazhan with general early vigor. For seed traits, Yuxiangyouzhan had lower seed hull weight but higher seed amylose content, seed amylase activity, and plumule–radicle ratio than Huanghuazhan, and consequently, Yuxiangyouzhan had about 10% higher germination percentage and velocity and 37% longer plumule than Huanghuazhan. For seedling traits, leaf area, specific leaf weight, leaf chlorophyll and soluble protein contents, leaf net photosynthetic rate, and shoot–root ratio were higher in Yuxiangyouzhan than in Huanghuazhan, and as a result, seedling shoot biomass was 23–32% higher in Yuxiangyouzhan than in Huanghuazhan. These results indicate that Yuxiangyouzhan has both superior seed and seedling vigor. The former is attributed to the low mechanical strength of seed hull, high conversion efficiency of seed reserve, and high mobilization of seed reserve to plumule, while the latter is due to large leaf area, high leaf photosynthetic capacity, and high partitioning of dry matter to shoot. This study enriches the physiological understanding of superior early vigor in rice.

Apomixis Allows the Transgenerational Fixation of Phenotypes in Hybrid Plants

The introduction of apomixis-asexual reproduction through seeds-into crop plants is considered the holy grail of agriculture, as it would provide a mechanism to maintain agriculturally important phenotypes [1, 2]. Apomicts produce clonal offspring, such that apomixis could be used to transgenerationally fix any genotype, including that of F1 hybrids, which are used in agriculture due to their superior vigor and yield [3-9]. However, traits (phenotypes) do not only result from a complex combination of genetic and environmental variation but can also be influenced by epigenetic variation, which can be transgenerationally heritable in plants [10-15]. Hence, it is far from clear whether genetic fixation by apomixis suffices to fix the agriculturally relevant phenotypes of F1 hybrids, in particular because hybridization was recently shown to induce epigenetic changes [16, 17]. Here, we show that the phenotypes of Hieracium pilosella hybrids can be fixed across generations by apomixis. Using a natural apomict, we created 11 hybrid genotypes (lines). In these and a parental line, we analyzed 20 phenotypic traits that are related to plant growth and reproduction. Of the 20 traits, 18 (90%) were stably inherited over two apomictic generations, grown at the same time in a randomized design, in 11 of the 12 lines. Although one hybrid line showed phenotypic instability, our results provide a fundamental proof of principle, demonstrating that apomixis can indeed be used in plant breeding and seed production to fix complex, quantitative phenotypes across generations.

Effects of Plant Growth Promoting Rhizobacteria on Seed Germination Characteristics of Tomato and Lettuce

Plant growth promoting rhizobacteria (PGPR) represent a wide genera of rhizospheric bacteria which, when introduced in association with the host plant in proper amount, can enhance plant growth and productivity. A series of experiments were conducted to determine the germination responses of tomato and lettuce to PGPR inoculation. Seeds were inoculated with different strains of Azospirillum brasilense Sp7, Sp7-S and Sp245, Herbaspirillum seropedicea and Burkholderia phytofirmans PsJNT. The results reveal that Sp7-S inoculation yielded better germination rate and total germination of tomato. PGPR inoculation, except Sp7, produced longer (28%) and heavier (37%) roots with superior vigor. In lettuce, PGPR strains, except B. phytofirmans PsJNT, and Sp7 and B. phytofirmans PsJNT, enhanced germination vigor and length of roots (26%), respectively. The results provide further evidence concerning their importance as PGPR and indicate the potential of exploiting some of these PGPR to improve seedling emergence and establishment of vegetables.

Genetic Variation for Achene Traits in Cup Plant (<i>Silphium perfoliatum</i> L.)

Cup plant (Silphium perfoliatum L.) has demonstrated potential for biomass production in studies using transplants in poorly drained cropland not suitable for conventional crops, but little is known about its establishment from seeding. The success rate for stand establishment of perennial plants is usually positively correlated with seed weight. Therefore, objectives of this study were to determine contribution of genetic effects to variation in achene weight, seed weight, achene length, and achene width of cup plant in a population with high biomass potential. Seedlings of 33 half-sib (HS) families were transplanted at Brookings, SD in 1999 and 2010. Achene/seed traits were determined at seed maturity in 2000, 2011 and 2012. Narrow-sense heritability was higher for achene weight and seed weight than that for dimensional achene traits. Within-population genetic variation occurred for achene and seed weight, both of which varied in response to temporal variation in precipitation and temperature. Results of this study indicated the presence of sufficient additive genetic variation for progress from among-family selection for achene weight. Thus, since families with heavy achenes had higher percent seedling emergence and superior seedling vigor compared to families with light achenes, achene weight may be useful for indirect selection for enhanced seed quality in development of new cultivars of cup plant for biomass production on marginal crop land.

Seed and Seedling Vigour in Tropical Maize Inbred Lines

Abstract Seed and seedling vigour is an aspect of seed quality which affects field establishment and performance. Low maize yields have been reported to be affected by several factors in which poor quality seed with low seed and seedling vigour. Information is scarce on seed and seedling vigour in maize inbred lines developed for tropical environments. Fifteen genotypes of tropical maize (Zea mays L.) inbred lines were evaluated to determine the level of differences in seed and seedling vigour traits, and extent of relationships among traits and their heritability. A substantial amount of genetic variability was found, which suggested that most of the traits under study could be improved through selection and utilized in breeding programs. Positive and significant interrelationship among seed germination and seedling traits and a positive correlation between seed germination and seed vigour and field emergence showed that these could be given due consideration in crop improvement for seed and seedling vigour. High genotypic coefficient of variation, heritability and genetic advance were obtained for seed germination, seed emergence, shoot length and seedling vigour index I and II, revealing the possibility of improvement in these characters through direct selection. The principal component analysis (PCA) identified seed emergence, shoot length, seedling vigour index I and II and tetrazolium vigour as characters that contributed greatly to variation in seed vigour in the maize inbred lines. Cluster analysis partitioned the genotypes into two groups, with group I consisting of seven genotypes and group II comprised the other eight genotypes, which suggested that hybridization between the two groups could lead to high level of heterosis. Genotype V5 had superior seedling vigour traits compared to other genotypes. Seedling emergence, shoot length, seedling vigour index I, seedling vigour index II and tetrazolium vigour are effective characters for good seedling vigour traits in maize inbred lines investigated.

The flowering gene SINGLE FLOWER TRUSS drives heterosis for yield in tomato

Intercrossing different varieties of plants frequently produces hybrid offspring with superior vigor and increased yields, in a poorly understood phenomenon known as heterosis. One classical unproven model for heterosis is overdominance, which posits in its simplest form that improved vigor can result from a single heterozygous gene. Here we report that heterozygosity for tomato loss-of-function alleles of SINGLE FLOWER TRUSS (SFT), which is the genetic originator of the flowering hormone florigen, increases yield by up to 60%. Yield overdominance from SFT heterozygosity is robust, occurring in distinct genetic backgrounds and environments. We show that several traits integrate pleiotropically to drive heterosis in a multiplicative manner, and these effects derive from a suppression of growth termination mediated by SELF PRUNING (SP), an antagonist of SFT. Our findings provide the first example of a single overdominant gene for yield and suggest that single heterozygous mutations may improve productivity in other agricultural organisms.

Population structure, flowering and seed production in the endangered Whibley wattle, Acacia whibleyana (Leguminosae: Mimosoideae).

Acacia whibleyana (Whibley wattle) is a nationally endangered wattle, endemic to the near-coastal region around Tumby Bay on the Eyre Peninsula in South Australia. Two distinct sub-populations, referred to as the Quarry and the Salt-lake populations, each contained plants growing on roadsides and in scrub fragments. Marked differences were observed in the population size structure between the two populations. The absence of juveniles on roadsides in both populations signaled potential limitations to natural recruitment. Studies of reproductive biology of scrub plants over two years (1996-1997) indicated that between 1.1% (Salt-lake) and 6.9% (Quarry) of A. whibleyana inflorescences produced fruit. Each infructescence produced an average of 1.2-1.8 pods, although up to 10 pods per infructescence were observed at the Quarry scrub in 1996. Each pod contained 4-6 seed on average, with a viability of 85%. Plants at the Salt-lake scrub generally set less fruit, produced fewer pods per infructescence, and had lower seed numbers per pod when compared with Quarry plants, differences attributable to the superior vigor of Quarry plants. A. whibleyana seeds were dispersed by ants attracted by the lipid-rich aril. The soil seed bank had a patchy distribution across both sites possibly due to seed concen- trating in the vicinity of ant nests. We concluded that the reproductive attributes studied were unlikely to constrain natural recruitment of A. whibleyana as both populations were capable of producing viable seed over the two years of this study.

Swiss maize landraces - Early vigour adaptation to cool conditions

Due to their good early vigour, Swiss maize landraces have been used extensively to develop the Flint Pool of European hybrid-breeding programmes. However, the basis of good early vigour, especially under cool conditions, has not been elucidated. Of 166 pre-screened Swiss maize landraces, 17 contrasting accessions were tested together with two control accessions, a German landrace and a modern hybrid cultivar with proven good early vigour, at sites in the midlands and the foothills of the Alps in Switzerland. To investigate early vigour, photosynthesis, leaf greenness and plant growth were recorded. Compared to the modern standard hybrid cultivar, northern accessions showed superior early vigour under cold stress in the field for all traits examined in these experiments, whereas these traits were much less pronounced in southern accessions. In particular, some accessions from the Rhine valley seem to be promising sources of early vigour for use in breeding programmes. These findings support the hypothesis that long-term selection resulted in the adaptation of maize landraces to their local environment. Compared to the phylogenetic tree, it is evident that accessions with superior early vigour are related to each other and originated in the Rhine valley.

'Florida Moonlight'—A White Fancyleaved Caladium for Pots and Shady Landscapes

Caladiums [Caladium bicolor (Ait.) Vent., syn. Caladium×hortulanum Birdsey, Araceae Juss.] are tropical foliage plants asexually propagated from tubers. Most of the world s tubers are produced in Highlands County in Central Florida on the muck and sandy soils around Lake Placid and Sebring. The industry plays a vital role in the local economy, with a wholesale crop worth $11–14 million annually, produced on 567 ha (Bell and Wilfret, 1998). The caladium industry also plays an important sociological role in Highlands County. Lake Placid is known as the caladium capital of the world and caladiums are an integral part of the art and history of the community. The area celebrated its 12th annual caladium festival in Aug. 2002. The Univ. of Florida initiated a caladiumbreeding program in 1976 at the Gulf Coast Research and Education Center (REC)–Bradenton under the leadership of Gary Wilfret. The program s goal was to develop new cultivars for the industry, which had not had new introductions since the 1950s. In addition to developing new landscape-type cultivars, the program has sought to develop cultivars better adapted for container production, with shorter petioles, multi-eyed tubers, and increased leaf production. Twelve cultivars have been released since 1976: ‘Florida Cardinal (Wilfret, 1988a), ‘Florida Roselight (Wilfret, 1988b), ‘Florida Sunrise (Wilfret, 1988c), ‘Florida Elise (Wilfret, 1991a), ‘Florida Fantasy (Wilfret, 1991b), ‘Florida Sweetheart (Wilfret, 1991c), ‘Florida Calypso (Wilfret, 1995), ‘Florida Irish Lace (Wilfret, unpublished release in 1999), ‘Florida Red Ruffles (Wilfret, unpublished release in 1999), ‘Florida Blizzard (Harbaugh et al., 2002), ‘Florida White Ruffles (Miranda et al., 2002), and ‘Florida Whitewater (Wilfret et al., 2002). ‘Florida Moonlight represents the first release from the Univ. of Florida in the ‘June Bride type, characterized by large, white, heart-shaped leaves and white primary veins. ‘June Bride , although producing attractive foliage, represents only 1% of caladium tuber production in Florida (Bell and Wilfret, 1988), in part because of poor performance in containers. ‘Florida Moonlight (Fig. 1) has demonstrated the potential to produce a superior number of leaves that emerge sooner compared to ‘June Bride , and to produce an attractive plant in a 10-cm container when buds are excised (Evans et al., 1992). In addition, ‘Florida Moonlight has demonstrated superior vigor to ‘June Bride when grown in outdoor landscapes.

Restoring depleted Tunisian drylands with native species: Where should we source the seeds?

In many of the world's drylands genetic and soil erosionare widespread. To enhance success of any large scale restorationeffort in these hazardous conditions, it is essential to set upsystematic seed production of key native plant species. The aim ofthe traditional outline is to gather local yet ample geneticvariation to avoid the risks of non-adaptation. But forStipa lagascae R. and Sch, aNorth-African perennial bunch grass, we carried out an outlineinspired from conventional forage breeding practice, with the aim toselect for vigour. Here, we assess its outcomes as for the risk ofselecting non-local and/or non-ample geneticvariation. We established a collection composed of 276 clonal linesout of individuals coming from 70 accessions, spread over 6 majorecogeographic origins within Presaharian Tunisia (100mm < average annual rainfall < 200mm), both source and target region. During 7successive growing seasons with stark contrasts for rainfall andfertility, we observed the collection for vigour and phenology.Principal Components Analysis has been carried out on a data matrixof 276 lines and 11 variables. Both for vigour and for phenology,individuals differentiated strongly, but irrespective of accession orecogeographic origin. Moreover, differences for vigour persistedthroughout contrasting growing seasons. Both facts combined(1) do not indicate any local adaptation within the targetregion, (2) suggest instead intense genetic structuring dueto isolation by distance, (3) make it easy to cull alimited number of lines to combine considerable genetic variationwith consistently superior vigour.

Hybrid poplars: present status and potential in Britain

Past and potential future use of hybrid poplars for wood production in Britain is considered, and preliminary results of trials with new clones imported from Belgium in 1985 are given. A series of nine field experiments established in 1991, to a common protocol, was analysed using stepwise multiple regression. The superior vigour of 'Beaupre' compared with 'Ghoy', 'Robusta' and 'Trichobel' was clear in almost every case. For 'Beaupre' (Populus trichocarpa X P. deltoides) altitude emerged as the variable explaining most variation in tree height after six growing seasons, height declining with increasing altitude. The four best sites were characterized by low elevation and low rainfall. At the two older sites planted in 1987, at Ampthill and Bedgebury, the 'interamerican' hybrids (P. trichocarpa X P. deltoides) were the most vigorous, and the clones 'UnaP and 'Raspalje', which were thought to be too rust susceptible to release for commercial use in 1990, achieved similar stem sizes to those of 'Beaupre' and 'Bolelare'. The General Yield Class (based on a reference spacing of 8 X 8 m) calculated for 'Beaupre' was 8 at Ampthill and 24 at Bedgebury. Future prospects for poplar planting are considered in relation to possible reform of the Common Agricultural Policy.