Callose depositions underlie the incompatible reaction in intergeneric crosses of rice

Distant hybridization of cereals is often impaired by fertilization barriers. Haploid induction through intergeneric crossing is well developed in wheat but has not been successful in rice due to incompatibility issues. The present study was thus undertaken to identify fertilization barriers that hinder the compatibility of the rice cultivar Punjab Rice 121 with maize and pearl millet lines as pollinators. A total of 37,357 spikelets were pollinated, yielding 494 caryopses upon supplementation with auxins. The resultant caryopses, arising from true intergeneric crosses, lacked embryos. Imaging of the pollinated pistils at different intervals indicated that intense callose depositions block the release of generative nuclei to the ovule in these wide crosses. Rice spikelets pollinated with rice pollen (cis-generic crosses) exhibited positive indicators of fertilization reaction at the micropyle. While the cis-generic crosses initiated true caryopsis formation after 24 h, no comparative reaction was observed in the intergeneric crosses. The current survey underlines that the rice female gametophyte presents a strong pre-fertilization barrier to foreign pollen. This barrier may be modulated in the future by altering genotype and auxin combinations.

Mycelial growth variation and compatibility of the selected isolates of Bipolaris sorokiniana (Sacc.) Shoemaker

Bipolaris sorokiniana (Sacc.) Shoemaker is a phytopathogenic fungus, causal agent of leaf blight disease of wheat. This fungus is difficult to control because of its immense cultural, morphological, physiological, pathogenic and genetic variability. The aim of this investigation was to study the cultural variability of the selected isolates of B. sorokiniana by means of mycelial compatibility. One hundred fifty isolates of B. sorokiniana from eight districts (Dhaka, Gazipur, Dinajpur, Joypurhat, Pabna, Sirajgonj, Kushtia and Chuadanga) of Bangladesh were studied and cultural variation was characterized on the basis of colony color and texture on PDA medium. They were - Black-Mat (B-M), Black-Fluffy (B-F), Ash-Mat (A-M), Brownish Ash-Fluffy (Br. A-F), Blackish Ash-Mat (Bl.AM), Whitish Ash-Mat (W. A-M), Greenish Ash-Fluffy (G. A-F) and Pinkish White-Mat (P.W-M). To compare and understand cultural variability, mycelial compatibility test was done among the cultural groups. Results revealed that selected isolates of different cultural groups showed incompatible reaction. Incompatibility was also noticed between the isolates of same district and different districts. Dhaka Univ. J. Biol. Sci. 28(2): 195-209, 2019 (July)