Results
Seed Set: After crossing wheat x maize, so called seed-like structures (here we call seed) were formed, which showed embryo formation (Fig. 1a). For seed set, analysis of variance among the wheat genotypes W1-W5 showed a significant F-value (Table 2). Comparison of means showed that among these five genotypes, W1-W4 fell in the same class, while W5 had a significantly smaller mean (Table 3). The smaller mean response of W5 might have arisen from insufficient reception of hormone (probably 2,4-D), which is crucial for enlargement of ovary or seed set. Percentage of embryo formation: There was a highly significant F-value for genotypes suggesting that at least two wheat parents significantly differed in haploid embryo production rate (Table 2). For this trait, mean comparison showed that W1 with an average of 12.8% was the most superior genotype followed by W3 (9.7%) and three other genotypes (Table 3). W2 with 2.5% embryo formation rate was the poorest genotype.
The range of embryo formation was 5.1-17.5% for W1, 1.2 -4. 1% for W2, 6.2-12.6% for W3, 0.0-9.7% for W4 and 2.2-9.0% for W5. The overall average across the five genotypes was 9.2%.
Embryo germination rate: Out of 366, cultured embryos, 227 (62%) germinated and started development of shoots and roots (Table 3). Three wheat genotypes W1, W3 and W5 were more successful in embryo production than the other two, therefore they were used for study of the genotypic influence on embryo germination rate and plantlet recovery. According to ANOVA result for embryo germination rate, there was no significant difference among the genotypes, suggesting that germination of the cultured embryos was not directly affected by their wheat parents. But the means of these three genotypes (Table 3) show a smaller value for W5, which showed also a lower percentage of embryo formation in comparison to W1 and W3.
Plantlet recovery: From 227 germinated embryos only 104 produced plantlets of 5-15 cm in length suitable for transplanting in pots (Fig. 1b). The rest of embryos showed a slow development of plantlets and mostly they stopped growth later. Plantlet recovery also showed no significant F-value for variation among genotypes (Table 3). It was observed that some embryos germinated but did not develop to green plantlets. Chromosome counting of the mitotic root cells confirmed haploidy of the regenerated plantlets (Fig. 1c). The average percentage of plantlet recovery over the five genotypes was 28.4% of cultured embryos.
Pollen tube studies: Pollen tube studies showed that within 30 minutes of pollination, maize pollen tube has already penetrated the lateral branches of wheat stigma and 1 hour after pollination the, longest maize pollen tubes have entered the main axis of stigma. For the measurement of the length of pollen tube, only samples of 30 minutes after pollination were used because the more developed pollen tubes (after 30 minutes) were not suitable due to their entering to the main axis of stigma wings and ovary.
Result of t-analysis for pollen tube length of W1 and W5 crosses showed a highly significant difference between their means showing that the growth speed of maize pollen tube was not equal in stigma of these two wheat genotypes. The mean of pollen tube length in crosses of W1 was greater (faster growth) than that of W5 crosses (Table 4). This was in agreement with their performance for percentage of embryo formation suggesting that the genotype of W5 is responsible for slower growth of maize pollen tube and less percentage of embryo formation.