Dwarf Hybrids Research Articles

Assessment of Germination Response to Salinity Stress in Castor through the Hydrotime Model

Germination of castor seeds from five dwarf hybrid genotypes, compared to a ‘Local’ genotype selected by the University of Catania from a Tunisian population well adapted to the Mediterranean environment, was studied at five different salt levels (0, −0.3, −0.6, −0.9, and −1.2 MPa) in order to assess seed germination performance under stress conditions. The results confirmed that optimum moisture (0 MPa) ensured 100% of germination; on the contrary, salt concentration negatively influenced the final germination percentage (FGP) and radicle elongation, causing severe consequences for plant establishment. At a level of −1.2 MPa, no germination occurred, while a level of −0.3 MPa slightly affected the seed germination of the dwarf genotypes, which achieved 77.3% of germination, contrary to the ‘Local’ genotype, in which germination was kept stable. Higher levels of salt (−0.6 and −0.9 MPa) caused a linear decrease in FGP and radicle elongation. Overall, the dwarf hybrid ‘C1019’ performed better at higher salt impositions, as did ‘C857’, confirming these genotypes were the most tolerant among the dwarf hybrids. Conversely, ‘C1013’ turned out to be the most susceptible genotype, followed by ‘C1008’. On the other hand, the ‘Local’ castor genotype was the best-performing genotype at −0.3 MPa and the most tolerant genotype in terms of salt concentration and germination time, which were accurately predicted by the hydrotime model, validating it as a valid method of assessing the germination response of castor seeds to Ψ.

Germination Response of Different Castor Bean Genotypes to Temperature for Early and Late Sowing Adaptation in the Mediterranean Regions

Germination of castor seeds of seven dwarf hybrid genotypes, compared to a ‘Local’ genotype, selected from a Tunisian population by the University of Catania well adapted to the Mediterranean environment, were studied at six different temperatures (8, 12, 16, 25, 32, and 40 °C). The results indicate that the optimal temperature (25 °C) and near-optimal temperature (32 °C) are the best temperatures for ensuring castor germination (final germination percentage (FGP) ≥ 82.81%). Furthermore, these temperatures positively influenced the vigour index (VI) and the radicle elongation. At a temperature of 8 °C, no germination occurred, while temperatures of 12 and 40 °C negatively affected the seed germination, which, in some genotypes, was null or negligible (<21.25%). A temperature of 16 °C allowed good results to be reached for the FGP and the other considered parameters. Overall, the dwarf hybrids performed better at high temperatures than at low temperatures, thus, making them suitable for late sowings, with the exception of the genotype ‘C1020’, which resulted the best performance at 16 and 40 °C, being suitable for both early and late sowings. On the other hand, the ‘Local’ castor genotype, being the best-performing genotype at 12 and 16 °C, and the most tolerant to low temperature (base temperature (Tb) 12.1 °C), could be used in the early sowing in spring.

Conventional and modern breeding technologies for improving dwarf coconut cultivars: A review

ABSTRACT Coconut (Cocos nuciferaL.) is a multipurpose plantation crop with versatile uses, including as a refreshing drink, edible oil, and, nutraceuticals. Its nutraceutical properties have increased demand in global markets. However, coconut productivity remains low owing to inadequate improved planting materials. This challenge has created a high demand and low supply gap in the coconut industry, which needs to be addressed through breeding methods that can increase productive cultivars in a shorter time. Breeding methods, such as mass selection and hybridization between dwarf and tall cultivars, are the main coconut improvement methods because of their simplicity and ease of use. The hybrids produced, however, take a long time (4-6 years) to bear fruits due to genes inherited from tall parents. Dwarf hybrids that bear fruits in a shorter time (3 years) are less exploited. Developing these coconut types through efficient breeding methods can fill the supply and demand gaps created in the coconut industry. Marker-assisted selection and multi-omics, have been used to identify quantitative traits of agronomic importance to increase genetic gains in dwarf coconut cultivars. This review article summarizes the advances in coconut improvement through conventional breeding, marker-assisted selection, and multi-omics approaches, focusing on dwarf coconut cultivars.

Genetic Variation among Varieties, Wild Species and Related Genera of Arecanut (Areca catechu L.) as Revealed by Microsatellite Markers

Studies on genetic diversity of crops are crucial for germplasm conservation and crop improvement programmes. Arecanut (Areca catechu L.) is one of the plantation crops that have been in cultivation since time immemorial in tropical regions of the world. In this investigation, molecular characterization and genetic diversity analysis was carried out among 20 arecanut genotypes comprising of 16 cultivated types (including 13 cultivated varieties, two dwarf hybrids and a natural mutant), two wild species (Areca triandra and Areca concinna) and two other genera (Normanbya normanbyii and Actinorhytis calapparia), maintained in the National Arecanut Gene Bank, Vittal, Karnataka State, India, by employing eight simple sequence repeat (SSR) markers. A total of 45 alleles were detected with most of the markers revealing five alleles or more. The number of alleles at each locus varied from 3 (AC07 and AC08) to 8 (AC23) with a mean of 5.62 alleles per locus. The polymorphism information content (PIC) value, which is a measure of polymorphism for a marker locus, varied from 0.46 (AC08) to 0.84 (AC01) among the SSR markers loci, the average being 0.70. The effective number of alleles per locus (Ne) ranged from 1.28 to 3.11 with a mean of 2.31. The marker AC07 had the lowest effective number of alleles per locus and the marker AC29 had the highest numbers of effective alleles. Shannon’s Information Index ranged from 0.43 (AC07) to 1.33 (AC23) with a mean of 0.97. The observed heterozygosity (Ho) values ranged from 0.25 to 1.00 with an average of 0.73. The expected heterozygosity (He) values ranged from 0.22 to 0.69 with an average of 0.54. The degree of genetic differentiation among the subpopulations (FST) ranged from 0.11 (AC06) to 0.66 (AC01) with a mean of 0.32. The gene flow (Nm) values ranged from 0.12 (AC01) to 1.96 (AC06) with a mean gene flow value of 0.52. The lowest gene flow value was observed in the marker AC01 and the highest gene flow was exhibited by AC06. The dendrogram constructed using similarity coefficient values, by following the Unweighted Pair Group Method with Arithmetic Mean (UPGMA), formed two major clusters with cluster I consisting of all the 16 cultivated varieties and 2 wild species, viz., Areca triandra and Areca concinna and the second major cluster comprised of related genera viz., Normanbya normanbyii and Actinorhytis calapparia. The highest genetic similarity was observed between the cultivated varieties, Kahikuchi and Mohitnagar and Nalbari and Sumangala, and the lowest similarity value of 0.33 was found between the related genera, Normanbya normanbyii, and the cultivated variety, Sreemangala.

Effectiveness of Three Terminating Products on Reducing the Residual Moisture in Dwarf Castor Plants: A Preliminary Study of Direct Mechanical Harvesting in Central Greece

The contribution of castor oil for reaching the targets set by RED1 and RED2 in Europe can be tangible if the problem related to the mechanical harvesting is overcome. Dwarf hybrids suitable for mechanical harvesting are already available on the market but the residual moisture of plants and capsules has to be lowered in order to allow mechanization. In the present case of study, three common terminating products (Glyphosate GLY, Diquat DIQ and Spotlight DEF) were tested on Kaiima C1012 hybrid in a complete randomized block design to assess the effectiveness of using chemical products to decrease residual moisture in castor plants. Plants were harvested via combine harvester equipped with cereal header to evaluate seed loss (due to dehiscence, impact and cleaning shoe) and the dehulling capacity of the combine harvester’s cleaning shoe. DIQ decreased significantly moisture content of capsules (7.32%) in comparison to the other treatments, while the lowest plant moisture was recorded in DIQ (62.38%) and GLY (59.12%). The use of DIQ triggered the highest impact seed loss (61.75%) in comparison with GLY (46.50%) and DEF (29.02%). Control plants could not be harvested mechanically due to the high residual moisture content and high density of weeds. The present case of study provides highlights regarding the need to further investigate the best practice to terminate castor plants and to develop a specific combine header to reduce seed loss from impact.

English

A diallel cross was produced using diverse maize (Zea mays L.) germplasm of saline tolerant and saline susceptible maize lines as parents. Agronomic performance of the offspring of the diallel cross was examined. Eight germplasm lines bearing diversified agronomic traits of five known tolerant and susceptible lines were involved as parents of the diallel cross that was evaluated at three different ecological areas viz. Gazipur, Benerpota, and Kaliganj. CZ-29 and CZ-26 had positive and significant general combining ability (GCA) effects for yield in both the saline environments, where CZ-12 possessed negative and significant GCA effects for yield in the same areas but none of the parents exhibited either significantly positive or negative GCA in Gazipur location. Of the saline tolerant lines evaluated, CZ-29 was a good source for increased yield with significant and positive GCA values in both the saline environments that was also responsible for dwarfness and earliness in all locations. CZ-26×CZ-24 yielded well except at Benerpota with an additional benefit of shorter plant type across all environments. Hybrid CZ-29×BIL-65, however, was consistent and promising over the environments for bold seed and higher yield that ranked 2nd at Benerpota (4.81 t ha-1) and Kaliganj (6.73 t ha-1) and 3rd at Gazipur (7.40 t ha-1) location for yield having significant positive specific combining ability (SCA) effects at Gazipur and Kaliganj. Moreover, six hybrids either significantly or not consistently decreased yield over the locations with negative SCA. However, considering the overall performance of the hybrids, the involvement of saline susceptible or tolerant parents was not consistent in the present study. Crosses between saline tolerant lines did not produce any tolerant hybrids or dwarf parents did not produce dwarf hybrids except CZ-29×CZ-36 that was able to produce shorter hybrid for all the locations. Therefore, among the lines evaluated in this diallel cross having a distinct different genetic background, CZ-28 and CZ-29 contributed to earliness; CZ-29 and BIL-65 reduced plant height; CZ-12 increased seed size; CZ-26 and CZ-29 improved yield. Thus, these lines should be useful sources of alleles for pyramiding, earlier maturity, shorter plant heights, increased seed size and improved yield into desired breeding lines. Key words: Diallel, maize, saline, environments, general combining ability, specific combining ability.

Study of genetic diversity and identification of promising acceassions of arecanut (Areca Catechu L.)

The study was undertaken to assess and analysis of genetic diversity and to identify the donor parents with desirable traits among the selected 50 arecanut accessions including exotic and indigenous accessions by principal component analysis (PCA) method. The PCA of vegetative, reproductive, nut and yield characters indicated that the first 13 principal components accounted for 81.41 per cent of the variation among the accessions studied. The characters stem height, length of leaf, number of leaflets on right and left side, number of nodes, number of midribs on right side, male phase (days), female phase (days), intra-spadix overlapping (days), number of tertiary rachillae, fresh fruit weight, husk thickness in fresh fruit, dry kernel weight, dry fruit weight and kernel length were found to be contribute to genetic divergence among the arecanut accessions based on PCA. Based on their performance and genetic divergence, the accessions VTL-12 (Saigon), VTL-18III (BSI), VTL-29IV (Andaman), VTL-29II (Andaman), VTL-85 (Ratnagiri), VTL-73 (Kahikuchi), VTL-78 (Saragoan) and VTL-97 (Wynad) could be useful in arecanut breeding programmes. Accession VTL-56, a dwarf arecanut accession has been exploited in the breeding dwarf hybrids.

Occurrence in Brazil of Haplaxius crudus (Hemiptera: Cixiidae), Vector of Coconut Lethal Yellowing.

The lethal yellowing (LY) is a major phytoplasma causing disease seriously threatening coconut plantations worldwide, with imminent risk of entering Brazil. The LY phytoplasma is restricted to the phloem and transmitted by the planthopper Haplaxius crudus (Van Duzee) (Cixiidae). In this study, Auchenorrhyncha were collected on the leaves of Dwarf vs. Dwarf hybrids and Brazilian Green Dwarf Jiqui in the Brazilian northern state of Para using yellow adhesive traps in May of 2016. The planthopper H. crudus was found in coconut plantations of Brazilian Green Dwarf Jiqui, accounting for 87% of the individuals captured. This is the first report of vector H. crudus in Brazilian coconut plantations. These findings are of great scientific relevance since H. crudus could negatively impact the Brazilian coconut industry and this knowledge could be used in contingency measures in the case of LY be introduced in the country.

Selection of legitimate dwarf coconut hybrid seedlings using DNA fingerprinting

Abstract Due to the great economic importance of coconut palm in Brazil and the development of a coconut breeding program intended to produce intravarietal hybrids, the present work aimed to ease the production of hybrids with the same morphological heritage. DNA was extracted from leaf samples of 13 dwarf coconut populations from Brazil, and PCR amplification was performed using 21 previously selected microsatellites. Furthermore, this study selected nine microsatellite markers with the potential to identify Green Dwarf x Yellow Dwarf hybrids and 16 microsatellites with the potential to identify Red Dwarf x Yellow Dwarf hybrids. In conclusion, SSR marker based on DNA Fingerprinting allowed the accurate identification of legitimate intravarietal hybrids since, for those crosses, the methodology of identification based on seedling color is not a viable alternative.

Terminal drought and a d2 dwarfing gene affecting grain iron and zinc density in pearl millet

Pearl millet, predominantly a rainfed dryland crop, often encounters terminal drought in crop season. Grain hybrids grown in India are of medium to tall height, and majority of them are based on d2 dwarf seed-parents. Eight pairs of tall and d2 dwarf isogenic-lines, developed from two diverse composites, were evaluated under irrigated control and imposed terminal drought for two-years to examine the effect of d2 dwarfing gene and terminal drought on grain iron (Fe) and zinc (Zn) density. In general, terminal drought had a significant effect on increasing the Fe and Zn density, the d2 dwarfing gene or the linked gene block significantly decreased both micronutrients, with the magnitude of increase or decrease, respectively, dependent on the environment and genetic background of the isolines. Terminal drought has severe adverse impact on grain yield, but grains produced from such environments are likely to be more nutritious with respect to Fe and Zn density. The d2 dwarf hybrids are likely to be less nutritious than non-d2 hybrids with respect to Fe and Zn density. Whether the d2 dwarf seed parents with reduced Fe and Zn density presumably may adversely affect grain yield and micronutrient levels of even non-d2 hybrids developed on them, and this aspect merits further investigation.

Dwarf hybrids of the bioenergy crop Ricinus communis suitable for mechanized harvesting reveal differences in morpho-physiological characteristics and seed metabolic profiles

Ricinus communis, also known as castor bean or castor plant, is a crop that produces seeds containing non-edible oil used widely in the chemical industry and the bioenergy sector. Varieties or hybrids that are suitable for mechanized harvesting may diminish the production cost boosting large scale production of the crop in new areas. In this study, we describe extensively the morphological characteristics and the ex situ performance of four newly developed R. communis hybrids (H11, H12, H13, and H14) focusing on plant architecture in order to facilitate mechanized harvesting. In addition, hybrid germination rate at low and optimal temperature was evaluated aiming to determine a minimal temperature requirement for early spring sowing in temperate climates. Seed metabolic profiling using LC–MS/MS analysis revealed the presence of more than 60 different primary and secondary metabolites, at varied levels in each hybrid, including amino acids, fatty acids, flavonols, flavones, flavanones, phenyl propanoids and catecholamines such as dopamine, many of which are reported for the first time in this species.

Hybrid Testing and Variety Identification of Coconut (Cocos nucifera L.) in Sri Lanka Using Microsatellite Markers

Currently, there is no reliable method for confirmation of the identity of coconut cultivars and the legitimacy of coconut hybrids. This makes serious problems in coconut breeding and seed production as the identity of coconut cultivars/hybrids can only be approximated at the very late stages of the growth based on reproductive traits owing to long juvenile period and the perennial nature of coconut. A microsatellite (SSR) marker based approach was used to develop an identification method for coconut varieties; Sri Lanka Tall, Sri Lanka Green Dwarf and Sri Lanka Yellow Dwarf, the key parents in the breeding programmes and tall x dwarf hybrids among them, using 18 coconut specific SSR primers. The validity of using yellow colour petiole as a phenotypic marker for the identification of dwarf yellow was also investigated. Two SSR primers, namely CAC20 and CNZ6 have exhibited the potential for distinguishing coconut varieties used as parents in the breeding programme and for confirming hybridity. It was revealed that yellow colour petiole is not a reliable marker for identification of dwarf yellow variety.

Effects of nitrogen and plant density on dwarf sunflower hybrids

SUMMARY This research was carried out to determine the seed yield and some yield components of two dwarf hybrids as compared to one standard-height sunflower hybrid ( Helianthus annuus L.) at different nitrogen rates and planting densities. The study was carried out under natural rainfed conditions at the Thrace Agricultural Research Institute in Edirne-Turkey between 1999 and 2001. The experiments were set up in split-split plots in a randomized complete block design with three replications. The main plot treatments were three different-height sunflower hybrids, DW-1, DW-2, and Trakya-80. The sub plots were three levels of nitrogen, 0, 60, and 120 kg N/ha. The sub-sub plots were three planting densities, 10 × 70 (142,850 plants/ha), 15 × 70 (95,230 plants/ ha), and 20 × 70 cm (71,430 plants/ha). Based on marginal economic analyses, the economically optimal seed yield per hectare was obtained at 50 kg N/ ha for DW-1 and at 80 kg N/ha for DW-2 and Trakya-80. In all three hybrids, increasing plant densities decreased 1000-seed weight, hull percentage, and head diameter but increased test weight in natural rainfed conditions. The highest seed yield in both dwarf hybrids was obtained with the spacing of 15 × 70 cm (95,230 plants/ha). The results of this research show that nitrogen and plant density have significant effects on seed yield and some yield components of different-height sunflower hybrids.

Comportamento de cultivares de coqueiros anão e híbridos no Distrito Federal

O cultivo do coqueiro na região Centro-Oeste pode tornar-se importante opção devido à crescente demanda por água de coco e à necessidade de os produtores diversificarem as atividades e melhorarem a renda. A demanda é totalmente atendida até hoje pela oferta de frutos de outros estados, tendo sido comercializadas 1.700 t via CEASA-DF, em 1994. Apesar da importância econômica, a produtividade nacional é baixa pelo uso de genótipos não selecionados e pouca informação a respeito das práticas culturais.Com o objetivo de avaliar cultivares e híbridos de coqueiro quanto ao crescimento vegetativo, a Embrapa Cerrados-DF, em parceria com a Embrapa Tabuleiros Costeiros, desenvolve o experimento em delineamento de blocos ao acaso, com quatro e dois tratamentos, respectivamente, de cultivares e de híbridos, com três repetições. Os tratamentos foram as cultivares: Anão-vermelho-da-malásia, Anão-verde-de-jiqui, Anão-vermelho-de-camarões e Anão-vermelho-de-gramame, e os híbridos: Anão-amarelo-de-gramame x Gigante-do-oeste-africano e Anão-vermelho-de-gramame x Gigante-do-brasil-da-praia-do-forte. As plantas foram avaliadas quanto ao crescimento, à circunferência do coleto, ao número e ao comprimento de folhas. O objetivo desta pesquisa foi avaliar cultivares e híbridos de coqueiro quanto ao crescimento vegetativo, visando a indicar os materiais com melhor aptição para o cultivo no DF. Das cultivares, o 'Anão-verde-de-jiqui' vem-se destacando no crescimento e na circunferência do coleto, e, entre os híbridos, não houve diferença.

Root System and Water Use Patterns of Different Height Sunflower Cultivars

Dwarf sunflower (Helianthus annuus L.) cultivars have agronomic and management benefits over conventional standard height sunflower cultivars. However, the effects of reduced plant stature on root systems and water extraction characteristics are not known. Therefore, field trials were conducted at two locations in western Canada during 1994 and 1995 to compare root system characteristics and water extraction patterns of dwarf hybrids [two Sunwheat hybrids: ‘Sunwheat‐101’ (SW‐101) and ‘Sunwheat‐103’ (SW‐103)], and dwarf open pollinated cultivars [two Sunola cultivars, ‘AC‐Aurora’ (Aurora) and ‘AC‐Sierra’ (Sierra)] with standard height hybrids (IS‐6111 and SF‐187). Reducing plant height reduced rooting depth (by 0.20 to 0.60 m), root length density (by 6.6 m m−2) and root distribution in SW‐103 compared with IS‐6111, while no differences were observed in these traits between IS‐6111 and Aurora. The soil water depletion front velocities of sunflower cultivars were influenced by accumulated heat units, suggesting a temperature effect on rooting characteristics. IS‐6111 (0.14 to 0.19 cm growing degree d−1) and Aurora (0.15 to 0.17 cm growing degree d−1) had significantly higher depletion front velocities compared with SW‐103 (0.09 to 0.11 cm growing degree d−1). Greater soil water depletion by standard height hybrids in agronomy trials (average 59 and 79 mm more compared with dwarf hybrids and dwarf open pollinated cultivars, respectively) was attributed to deeper rooting depth (average 0.2 and 0.4 m more compared with dwarf hybrids and dwarf open pollinated cultivars, respectively) and more efficient water extraction, although a longer growth duration may also have been a factor.

Agronomic performance of different stature sunflower cultivars under different levels of interplant competition

Early-maturing, short-stature sunflower (Helianthus annuus L.) cultivars improve the adaptability of sunflower to the short growing season of western Canada. However, the agronomic potential of the recently developed dwarf cultivars in comparison to standard-height sunflower is yet to be understood. Multi-environment field studies, consisting of space-planted trials, where interplant competition was low, and agronomy trials, where plants were grown at commercial population densities, were conducted in southern Manitoba to compare the yield formation of dwarf hybrids (sunwheats; SW-101 and SW-103), and dwarf open-pollinated c ultivars (sunola; Aurora and Sierra) with that of standard-height cultivars (IS-6111 and SF-187). In space-planted trials, dry matter (DM) accumulation and water use efficiency for dry matter production (WUEDM) decreased as plant height decreased. In agronomy trials, differences in DM and WUEDM among the different height classes were masked. The diversion of assimilate from stem to head depended on the genetic background, while the efficiency of utilising assimilate in the head for seed production was lower in dwarf cultivars. Only one of the four dwarf cultivars (SW-103) displayed a higher harvest index than IS-6111. Higher seed yield for the standard-height cultivar, IS-6111, and the dwarf open-pollinated cultivar, Aurora, compared to other cultivars was attributed to both greater DM and improved DM partitioning. However, variations observed among the dwarf cultivars for DM accumulation and partitioning revealed that the dwarfing gene was not a limiting factor for breeding a dwarf sunflower cultivar with better partitioning of DM along with better yield potential. Key words: Dwarf sunflower, Sunola, seed yield, biomass, water use efficiency

Hybrid and Nitrogen Influence on Pearl Millet Production in Nebraska: Yield, Growth, and Nitrogen Uptake, and Nitrogen Use Efficiency

Pearl millet [Pennisetum glaucum (L.) R. Br.] is a staple grain crop in the arid and semiarid regions of Africa and India, and a new grain crop in the USA. A 2‐year field experiment was conducted near Mead, NE, in 1995 and 1996 on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudoll) soil with approximately 29 g kg−1 organic matter, 35 kg ha−1 NO3–N, and pH of 6.0. The objective was to determine the influence of hybrid and N on grain yield, dry matter accumulation and partitioning, and growth rates throughout the growing season. Nitrogen concentrations, uptake, and use efficiency were also determined. Treatments were a factorial combination of the pearl millet dwarf hybrids (59022A × 89‐0083, 1011A × 086R, and 1361M × 6Rm) and N levels (0 and 78 kg ha−1) in a randomized complete block design. Two plants per plot were sampled at 2‐wk intervals and partitioned into plant parts, dried, weighed, and analyzed for N concentration. Applied N increased grain yield by 0.4 to 0.5 Mg ha−1, but had only a small effect on dry matter accumulation and partitioning. Hybrid differences were small for grain yield. Pearl millet dry matter accumulation increased cubically in both years, with maximum crop growth rates among hybrids ranging from 0.48 to 0.57 g m−2 per growing degree day (GDD) in 1995 and ranging from 1.9 to 3.1 g m−2 GDD−1 maximum in 1996. The relative growth rate among hybrids declined from 0.012 to 0.020 g−1 m−2 GDD−1 in both years to near zero at physiological maturity. Nitrogen concentrations were higher during the vegetative stages and decreased with plant age. Applied N decreased N use efficiency for aboveground biomass (NUE1) by 18 to 25 g DM g−1 N, and N use efficiency for grain (NUE2) by 7 to 12 g grain g−1 N. Environmental variability due to years had a greater effect on yield, growth, and N levels than hybrid and applied N.

Inheritance of dwarfism in plantain (Musa spp., AAB group)

AbstractPlantain (Musa spp., AAB group) is a major food crop in the humid lowland tropics of Africa, the Caribbean and Latin America. Lodging, caused by strong winds occurs periodically in these areas. Therefore, development of dwarf plantain cultivars and elucidation of the inheritance of dwarfism is desirable. A heterozygous normal plantain cultivar (2n= 2x) with long false‐internodes (19.4 ± 0.9 cm) was crossed with a homozygous wild banana (2n= 2x) with short false‐internodes (6.9 ± 0.4 cm) to develop a test‐cross segregating population. A total of 74 euploids (2x, 3x and 4x) were produced. Forty‐one normal and 24 dwarf diploids were obtained, which fits a 2: 1 trisomic test‐cross segregation ratio for one locus. Dwarfism is controlled by a single recessive gene, dw. At the tetraploid level, two normal and six dwarf hybrids were produced, suggesting that the dw locus is close to the centromere and that there is a dosage effect of the dw allele at the tetraploid level.

XENIA EFFECT AND HYBRID VIGOUR IN COCONUTS

In coconut the dried endosperin known os the copra is the most important econontic product os it is from the copra, oil is extracted by crushing. To increase the copra content in coconut Haldane (1958) had suggested that it should be possible to compare the size, oil content and other characteristics of the nut borne on the same tree after using pollen from two different pollen parents. The also indicated that the hybrid vigour may possibly show in nuts derivedfrom cross pollination since hybrid vigour in some species is largely due to increased seed weight. If so, it is possible that a mixed plantation may produce a better crop than either of the two breeds when grown alone. Studies on the nut and copra characteristics of Tall x Dwarf hybrids and their reciprocals with their parents in coconut have indicated the importance of selection of pollen parents for producing proinising hybrids which will give better yields and also nuts of better quality and quantity of copra. Hence in copra improvement progrannne by hybridization, selection of parents is of great importance for the production of hybrids which will not only give high yield of nuts and also yield higher outturn of good quality copra. Attempts have been made to identify the best combinersfor the production of high yielding hybrids. Restilts obtained are dis­cussed in this paper.

A Test of the ‘Tall‐Dwarf” Hypothesis in Pearl Millet, Pennisetum glaucum (L.) R. Br.

AbstractPositive height‐grain yield relationships exist for many cereals, but cannot be fully used in breeding because of lodging and harvestability problems in tall cultivars. Law et al. (1978) proposed a “tall‐dwarf” hypothesis for wheat, in which the positive effects of minor height genes could be exploited by selecting for them in a major dwarfing gene background. The applicability of this hypothesis to pearl millet was tested by crossing a set of dwarf S1 progenies (from a single population) which varied in height onto two male‐sterile lines. Mean (by S1 pollinator) hybrid grain yield was closely related to mean hybrid height (r2= 0.60) over a range of mean yields of 3.0–3.9 t ha−1 and a range of mean heights of 126–165 cm. The effect of height was expressed as an increase in grain number in one cross and as an increase in grain mass in the other, indicating the importance of background genetic effects on yield‐height relationships in dwarf hybrids. The concept of “tall‐dwarfs” appears to be applicable to pearl millet.