Abstract only

The hybrid nature of necrosis was first studied by L.L. Dekaprelevich, the founder of Georgian school of genetics and breeding. Later on P. Naskidashvili applied tremendous effort to continue study of this phenomenon. Next steps in study of hybrid necrosis were made in works of I.A. Kostuchenko. In the 40-ies and the followed years ofthe last century, the works of Codwell and Koptin have been published, and in a short while the works of Heine. Interest to necrosis phenomenon has increa- sed recently. The large-scale studies have been carried out in relation to this phenomenon in the countries ofthe former Soviet republics, the Net- herlands and Japan. Hermsen Dutch scholar has greatly contri- buted to studies of necrosis phenomenon. He had confirmed the suggestion ofL.L. Dekaprelevich and I.A. Kostuchenko that hybrid necrosis is in many cases caused by two complementary genes and the wide variability of necrosis depend on the number of alleles of each gene of necrosis. Herrnsen has proved that the gene Ne l is bearing strong (s), moderate (m) and weak al1eles, while the gene Ne2 has strong (s), moderately strong (sm),moderately weak (mw) and finally, weak (w) al1eles. In addition to it, he had distinguished hybrid necrosis into the three groups according to its expression: 1. strong, when a plant is dead prior to the stage of tillering; 2. moderate, when a plant reaches the stage of heading, but is absolutely or partial1y sterile and the produced grain is friable (loose ); 3. weak, i.e. developed heading, the plant de- velops normal grain. The strength and the time of development stage when hybrid necrosis had been ascribed by Herrnsen to 8 stages, based on the following indica- tions: 1. a stage of the plant upon expression ofthe first symptoms of necrosis; 2. a stage of the plant with the most profound manifestation of necrosis; 3. grain weight in grams; 4. percentage of damaged area of two leaves of a plant upon completion of heading. Hermsen had offered the intensity scale of necrosis. Our studies have clearly proved that the first symptom of hybrid necrosis may be expressed at different plant development stages, namely at the stage ofl-2Ieaves, 2-3Ieaves, atthe stage of tillering or the stage of booting, prior to the stage of heading, during the stage of heading or upon its completion. Necrotic plant grows and develops noffi1ally, prior to manifestation of the necrosis symptom. Studies ascertained dependence of the phenomenon of necrosis on the activity of two complementary genes Ne 1 and Ne2. There are also contrary opinions that necrosis is a consequence of three domillating complementary activities, however majority of the scientists are in favor of the two dominant complementary gene theories. A Japanese scientist (Tsunevak, 1972) had through the method of monosomic analysis ascertained localization of the gene Ne 1 in chromosome 5B and of the geneNe2 in chromosome 2A. He also discovered the presence of necrosis genes in three chromosomes. A scholar of the same country, Nishikawa, had detected localization of the gene Ne2 in three chromosomes. The chromosomes 3B and 3D of wheat variety Chinese Spring carry genes of necrosis, whereas the right side of the chromosome 6B suppress development of necrosis. Presence of recessive modifiers also is suggested. Localization of two principal dominant complementary genes Ne 1 and Ne2 in the chromosomes 2B and 5B has been ascertained. Our studies have shown that varieties of wheat species Macha differ in genes of necrosis they carry. Three main genotypes have been ascertained in varieties of this species. Genotypes ofvarieties Colchicum and Lechkhumiucum as well as variety Paleoimereticum carry genes Ne 1 ne2. Genotype Ne 1 ne2Chl ch2 is carried by eight species of Macha (Ibericum, Lechkhumicum, Paleoimereticum, Paleocolchicum, Rubroveliticum, Rubiginesum, Sublechkhumicum, Colchicum), while genotype Nelne2chlch2 is inherent to two (Eristsiane, Paleoimereticum) and ne 1 ne2chl ch2 to three varieties (Lechkhumicum, Sharashidze, Megrelicum). Research has also ascertained the fact that the different individuals of the same variety may carry various genotypes. Some individual plants of variety Paleoimereticum, for example, have genotype Nelne2Chlch2 and Nelne2chlch2; there are also individual plants of Lechkhumicum carrying genotypes Nelne2Chlch2 and Nelne2chlch2. It was proved that the Ne 1 is inherent to almost all varieties of species of endemic Georgian wheat Macha, but they in no case carry the gene Ne2.

English

0409|AGRIS 0401|AL-Wheat Program

Juan Carlos Mendieta

CIMMYT Publications Collection