GrainGenes

I J Maureira; H Campos de Quiroz and H E Salvo*
Carillanca Regional Research Centre
PO Box 58-D, Temuco, CHILE
*: Corresponding author

Introduction

The interspecific cross H. vulgare L. X H. bulbosum L. is one of the most efficient systems for the production of haploid individuals in barley. The use of double haploid individuals in barley breeding allows a significant reduction in the breeding cycle as well as a most efficient use of resources. Furthermore, double haploid populations have been extensively used in the molecular mapping of barley, due to the advantages they possess when compared to other mapping populations. Nevertheless, in order to fulfill its potential, several stages of the process need to be further improved, and any potential bottleneck overcome. As part of an ongoing project aimed to develop double haploid barley populations and to maximize the yield of double haploid plants, we are currently studying a number of stages which may limit the production of double haploid plants through the bulbosum technique. This paper presents some of the results generated until now.

Material and Methods

Barley genotypes were crossed to H. bulbosum clones following the methodology of Furusho (1993). A total of 1937 seeds obtained through crosses involving 18 Chilean barley genotypes and 3 H. bulbosum clones were assessed, and the parameters number of embryos/seed, embryo size, and embryo quality studied. Embryos were classified in three different classes based upon their length (L1:>2.25 mm.; L2:2.25-1.25mm. and L3:<1.25mm.) and shape (S1:well differentiated embryo; S2:embryo with a slightly deformed scutellum, without clear meristems and S3:very irregular, globular embryos without any meristems). Linear correlation coefficients were calculated among the variables analyzed.

Results and Discussion

The Table 1 presents the correlation coefficients obtained (Table 1). A significant r value (P<0.05) coefficient was found between seed diameter and the number of embryos obtained per seed. Seeds with a diameter over 5 mm. are more likely to generate embryos (Figure 1), probably due to a higher amount of reserve tissues. It is also possible that larger embryos are more resilient to the stress caused by the dissection and tissue culture procedures than smaller, weaker ones. However, not every seed longer than 5 mm would generate a viable embryo, as reflected in the large scattering of the data points in Figure 1 and the very low or even negative r values determined between seed size and embryo quality.

TABLE 1. Linear correlation coefficients obtained between seed size and some embryo quality parameters (P<0.05)

The lack of clear relationships between seed development and embryo quality agrees with Thorn (1992), who suggested that seed development and embryo quality are regulated by different genetic systems. In other species such as Brassica napus different stages of the generation of microspore derived haploid plants are also regulated by different genetic systems (Dunwell, 1986). Kott and Kasha (1985) reported that differences in embryo features are even found among seeds derived from the same spike.

Factors such as growth regulators timing and concentration may also affect embryo quality. It is known that the differences observed in embryo development relate to endosperm abortion, and that yellowish, dried seeds often generate embryos showing inadequate development. In vivo observations indicate that proembryos not only depend on their reserves but also upon the endosperm for their nourishment (Thorn, 1993; Lopez, 1990). Furthermore, the barley genotype affects embryo seed and development (Thorn, 1992). Since embryo quality is closely related to embryo regenerability and subsequent plant development, it is important to establish which variables act upon it in order to maximize the production of haploid plants, since due to the breeding objectives pursued in many cases the selection of barley genotypes is fairly restricted.

Concluding, there was a moderately strong relationship between seed size and embryos per seed and a weak association between seed size and embryo quality. From a practical perspective, any seed longer than 5 mm should produce viable embryos, although whether or not these embryos would finally regenerate into haploid plants will depend upon other variables than seed size. A deeper understanding of the biology of embryo development would bring about improved in vitro regeneration strategies, which in turn will have a significant impact on the overall productivity of the bulbosum system and its wider application in barley breeding systems.

Acknowledgements

Financial support from the National Fund of Science and Technology (FONDECYT, Project 1950020) is gratefully acknowledged.

References

DUNWELL, J. 1986. Pollen, ovule and embryo culture as a tools in plant breeding. In: Withers, L. and Alderson, P. (eds.). Plant tissue culture and its agricultural applications. pp 375-403.

FURUSHO, M. 1993. Studies on haploid breeding for malting barley. Special Bulletin of the Fukuoka Agricultural Research Center No 7. Chikusino, Japan

KOTT, L. y K. KASHA. 1985. Embryo culture and haploid plant production. In Bright, S. and Jones, M. (eds.). Cereal Tissue and Cell Culture. Martinus Nijhoff/Dr W. Junk Publishers. pp 45-78.

LOPEZ, C. 1990. Cultivo de embriones y ovulos. In Fundamentos teorico-practicos del cultivo de tejidos vegetales. FAO, Chapingo, Mexico.pp 46-53.

THORN, E. 1992. The influence of genotype and environment on seed and embryo development in barley (Hordeum vulgare L.) after crossing with Hordeum bulbosum L. Euphytica. 59:1109-118.

-------. 1993. Embryo development in two barley genotypes after self pollination with Hordeum bulbosum L. Euphytica. 65:93-98.