Background Besides the Basmati, the aromatic rice germplasm (ARG) accessions are treasured for quality, medicinal value and aroma. The demand for aromatic rice is ever increasing. Genetic diversity is the source of variability to identify superior alleles controlling morphological, agronomic and quality traits, and molecular attributes. This study reports on the characterization of traits in ARG to identify a core set for breeding high-yielding varieties. Methods The genetic diversity was measured on the distinctness, uniformity and stability (DUS) of 46 traits in 208 Indian ARG in field, greenhouse and laboratory tests. We performed individual and combined analysis of DUS traits and molecular data generated using 55 SSR markers. The genetic distances between genotypes were estimated using Mahalanobis D2 analysis and clustering by standardized Euclidean2 distances, Ward Minimum variance, Gowers’ similarity index and PowerMarker. The aim was to derive a core set of non-Basmati ARG using PowerCore to deploy in crop improvement. Results Eighty-two alleles were detected. Alleles per marker ranged from 2 (RM505) to 5 (RM276) with an average of 3.04 alleles. The markers are informative in analyzing the diversity as the PIC values estimated varied from 0.17 (RM577 on chromosome 1) to 0.72 (RM276 on chromosome 6) with an average of 0.54 per locus. RM276 with repeat motif of (AG)8A3(GA) 33 on chromosome 6 was the most informative (amplified 5 alleles). The combined analysis had shown genotypes in a few clusters to be more diverse than others. SSR markers RM289, RM505, RM577 and RM22866 were identified as genotype specific markers. With PowerCore, 46 genotypes (22%) were identified as a core set of ARG that represent all the alleles detected in the entire set investigated. 2-Acetyl-1-pyrroline is considered to impart aroma; it was not detected by GC–MS tests in many ARG. Conclusions Forty-six genotypes in the core set have different maturity periods, plant statures, grain types and grain quality traits. A parent can be selected from the core set to improve aromatic rice depending on the breeding objective. The olfactory sensing of strong aroma emitted by cooked kernels of all ARG was found more decisive than the costly GC–MS tests.

Gall midge is the third most destructive insect pests of rice after stem borers and planthoppers. Host plant resistance has been recognized as the most effective and economic, means for gall midge management. With

Bacterial blight (BB) disease reduces the yield of rice varieties and hybrids considerably in many tropical rice growing countries like India. The present study highlights the development of durable BB resistance into the background of an elite maintainer of rice, DRR17B, by incorporating two major dominant genes, Xa21 and Xa33 through marker-assisted backcross breeding (MABB). Through two sets of backcrosses, the two BB resistance genes were transferred separately to DRR17B. In this process, at each stage of backcrossing, foreground selection was carried out for the target resistance genes and for non-fertility restorer alleles concerning the major fertility restorer genes Rf3 and Rf4, using gene-specific PCR-based markers, while background selection was done using a set of 61 and 64 parental polymorphic SSR markers respectively. Backcross derived lines possessing either Xa21 or Xa33 along with maximum genome recovery of DRR17B were identified at BC3F1 generation and selfed to develop BC3F2s. Plants harboring Xa21 or Xa33 in homozygous condition were identified among BC3F2s and were intercrossed with each other to combine both the genes. The intercross F1 plants (ICF1) were selfed and the intercross F2(ICF2) plants possessing both Xa21 and Xa33 in homozygous condition were identified with the help of markers. They were then advanced further by selfing until ICF4 generation. Selected ICF4 lines were evaluated for their resistance against BB with eight virulent isolates and for key agro-morphological traits. Six promising two-gene pyramiding lines of DRR17B with high level of BB resistance and agro-morphological attributes similar or superior to DRR17B with complete maintenance ability have been identified. These lines with elevated level of durable resistance may be handy tool for BB resistance breeding.

Genetic improvement of rice for grain micronutrients, viz., iron (Fe) and zinc (Zn) content is one of the important breeding objectives, in addition to yield improvement under the irrigated and aerobic ecosystems. In view of developing genetic resources for aerobic conditions, line (L) × tester (T) analysis was conducted with four restorers, four CMS lines and 16 hybrids. Both hybrids and parental lines were evaluated in irrigated and aerobic field conditions for grain yield, grain Fe and Zn content. General Combining Ability (GCA) effects of parents and Specific Combining Ability (SCA) effects of hybrids were observed to be contrasting for the micronutrient content in both the growing environments. The grain Fe and Zn content for parental lines were negatively correlated with grain yield in both the contrasting growing conditions. However, hybrids exhibited positive correlation for grain Fe and Zn with grain yield under limited water conditions. The magnitude of SCA mean squares was much higher than GCA mean squares implying preponderance of dominance gene action and also role of complementary non-allelic gene(s) interaction of parents and suitability of hybrids to the aerobic system. The testers HHZ12-SAL8-Y1-SAL1 (T1) and HHZ17-Y16-Y3-Y2 (T2) were identified as good combiners for grain Zn content under irrigated and aerobic conditions respectively.

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