Characterization of Guinea Grass Accessions (Megathyrsus Maximus) for Drought Tolerance

Abstract

Guinea grass (Panicum maximum Jacq., Megathyrsus maximus Jacq. Simon BK and Jacobs SWL) is one of the most productive perennial forage grass propagated through seeds. It is a desirable forage owing to its high nutritive value and resistance to adverse climatic conditions. However, its productivity is limited due to increasing drought periods as well as limited accessibility to improved varieties. The aim of this research work was to (i) To determine the genetic variation of the existing natural population of Guinea grass (M. maximus) accessions using simple sequence repeats markers (SSRs) and (ii) identify drought tolerant Guinea grass (M. maximus) accessions. To determine genetic diversity of the Guinea grass, thirty grass accessions previously collected from Nairobi, Kiambu, Muranga, Kilifi and CIAT gene bank in Colombia including three commercial cultivars namely Maasai, Mombasa and Tanzania were assembled from KALRO Field Gene Bank at Kakamega. The accessions were then grown in the greenhouse at KALRO-Muguga for multiplication to have sufficient germplasm. Tissues were collected from 2 weeks old leaves and extracted following modified CTAB method. Twenty-six Polymorphic Simple Sequence Repeat (SSR) markers previously isolated were utilize in determining the genetic variation and population structure of the 30 Guinea grass accessions. PCR amplicons were analyzed using PowerMarker software (Version 3.25) and MEGA software and 88.5% of the markers were highly polymorphic. Molecular cluster analysis based on Neighbor Joining revealed 2 main groups of accessions with wide variation within clusters and 88.5% of the markers were identified to be highly polymorphic. Results indicated that 95% of the variability was attributable to within groups and 5% variation among groups. The accessions were then evaluated across 2 environments namely KALRO Kiboko and Marigat in plots measuring 2.5m by 1.5m. The experiment was laid out in a randomized complete block design (RCBD) with split plot arrangement and replicated 3 times. Water regime was considered as the main factor while Guinea grass accessions were considered as sub-factor. Control plants were irrigated every 48 hours while drought stress was imposed by withholding irrigation water 25 days after clipping the grass. The plants under drought stress were irrigated once every 28 days until physiological maturity. Data on ground biomass weight, days to re-sprouting, plant height, leaf length, leaf width, days to flowering, panicle height, chlorophyll content, stand count and, number of nodes, tillers and flowered plants were collected from 10 plants. Means were separated using Tukey HSD and data analyzed using SAS software version 9.4, GEA-R software version 4.1, and META-R software version 6.0. GE interaction, GGE analysis and BLUPS were performed to rank the best performing accessions across the three environments. The results indicated significant (p≤0.001) effects due to Guinea grass accessions, environment, and their interactions for all traits measured. The accessions grown at Marigat produced the highest number of tillers, 19.5% above the mean compared to those grown at Kiboko. Highest broad sense heritability [H2] of 0.80 was recorded for germination and lowest value of 0.26 for stem diameter. From this study, accessions MK4, MK3, Maasai, 16019 and 6945 were tolerant to drought conditions and were found stable. These elite lines obtained in this study could be valuable for fodder breeding programs for the improvement of the forage productivity.