NARASIMHA RAO, K.L.RAVI BABU, M2020-02-282020-02-282019http://krishikosh.egranth.ac.in/handle/1/5810143867D5908An experiment entitled “Studies on leaf number index (LNI) in maize (Zea mays L.)” was under taken at the Agricultural College farm, Bapatla during two consecutive years of rabi 2016-17 and 2017-18. The crop growth stages of maize are dependent on various morphological, anatomical and physiological parameters. The basis for the variation in dry matter production and reproductive growth in relation to its foliage is less understood. The leaf growth that designates the physiological age of crop is more useful for crop improvement programmes. LNI is a tool to identify the exact time for the initiation of the reproductive stage by counting the number of leaves as the crop matures from vegetative stage to reproductive stage. So, the experiment was laid out in randomized block design with six maize hybrids viz., 900M Gold, DKC 9142, DKC 9120, DKC 9081, DKC 9042 and Pinnacle in four replications to identify the stage of reproductive growth in relation to the physical number of leaves on the stem, by calculating the leaf number index (LNI) corresponding to tassel and cob initiation and development. The observations were recorded for morphological, anatomical and physiological parameters at 7 days interval starting from 7 DAS. The results revealed that significant difference was observed among maize hybrids. Growing degree days (GDD) were measured for the crop growth seasons in 201617 and 2017-18, showed a gradual increase from 114.9 to 1447.5 and 141.6 to 1424.8 respectively from the 7 DAS till harvest. With the increase in GDD as the crop matures, plant height (12.43 to 274.5 cm and 11.88 to 268.75 cm), stem girth (0.21 to 2.84 cm and 019 to 2.88 cm), number of leaves per plant (3 to 16 in both the seasons) and LNI (20.31 to 100 % and 20.6 to 100 %) also showed a gradual increase in 2016-17 and 2017-18 respectively. Whereas, LAI showed an increase upto 70 DAS (0.05 to 5.68) during 201617 and till 63 DAS (0.04 to 5.65) during 2017-18 and then gradually decreased irrespective of GDD in both the seasons. During both the seasons, tassel primordial initiation coincided with the 9th visible leaf in 900 M Gold and DKC 9081, 10th visible leaf in DKC 9142 and Pinnacle and 11th visible leaf in DKC 9120 and DKC 9042 with LNI of 54.54, 54.54, 53.77, 52.79, 54.62 and 54.62 respectively in first season and 53.70, 54.71, 51.85, 53.70, 55.55 and 54.71 respectively in second season. Number of days to cob initiation in rabi 2016-17 was found less in DKC 9142 (32.25) followed by DKC 9120 (32.50), DKC 9042 (32.50) and Pinnacle (33.00) and high in other two hybrids 900M Gold and DKC 9081(43.75). In xvi second season it was 31.13 in DKC 9042, 32.00 in DKC 9142, 32.13 in Pinnacle, 32.63 in 900 M Gold and 34.00 in DKC 9081. All hybrids showed maximum level of chlorophyll (SCMR) at 63 DAS (first season) and 70 DAS (second season), high in Pinnacle and DKC 9142. This might be attributed to the LAI which was highest at 63 DAS and 70 DAS during 2016-17 and 2017-18 respectively. During rabi 2016-17 and 2017-18, DKC 9142 and Pinnacle recorded significantly higher photosynthetic rate and a sharp increase was noticed at 28 DAS. Higher net photosynthetic rate was recorded in maize hybrids at 70 DAS ranging from 37.80 to 39.95 (m mol CO2 m-2 s-1) but all hybrids were at a par. The physical number of the leaves on the stem were found to be 3 to 16 during both the seasons of the crop from 7 DAS until harvest. As the number of leaves increased, growth of the plant also showed significant changes with the rise of tassel and ear at 30 DAS and 33 DAS where the leaf number was 9 -11 during both the seasons. When the leaves on the stem are about 9-11, it readily indicates that the crop has entered the reproductive phase. Total dry matter highly accelerated at 63 DAS and DKC 9142 (220) recorded significantly more value. At 70 DAS, decreasing trend in stem, leaf, tassel and increasing in dry weight in cob and total dry matter was noticed in maize hybrids. Significantly higher dry weights were recorded by Pinnacle (116.00, 271.25) and DKC 9142 (115.52, 271.75) in respective cob and total dry matter at 77 DAS. Significant values were recorded by DKC 9142 and Pinnacle in root, cob and total dry matter (274.75 and 272.75) respectively. Dry matter partitioning of maize hybrids was different at different growth stages. Broadly it can be identified as four physiological stages i.e., vegetative stage (7 to 28 DAS), reproductive stage (28 to 42 DAS), grand growth stage (42 to 70 DAS) and physiologically mature stage (70 DAS to, harvest) where the dry matter varied from 0.4 to 5.4 and 0.31 to 5.63; 5.4 to 8.8 and 5.63 to 9.2; 8.8 to 274.75 and 9.2 to 266.3; 274.75 to 300.2 and 266.3 to 295 grams per plant during 2016-17 and 2017-18 respectively. CGR and NAR was found to be the highest at 57 to 63 DAS among all the hybrids during both the seasons where CGR was found to be the highest DKC 9142 followed by Pinnacle which were at par with each other. Whereas, pinnacle recorded highest NAR followed by DKC 9142. Among all the hybrids, RGR was found to be maximum at 50 to 56 DAS coinciding with reproductive primordial development. The yield and yield attributing characters such as length of the cob, number of rows per cob, number of kernels per row, 100 seed weight and the total kernel yield showed significant variation among the hybrids where the highest yield was obtained in pinnacle (9641.41 kg ha-1) and DKC 9142 (9243.9 kg ha-1). Leaf number index can be used as a tool to determine the correct stage to follow management practices within the crop which corresponds with the effective development of cob. A split dose application of nitrogen at 9 to 11th visible leaf stage is more effective corresponding to LNI ranging from 51.85 to 64.15 with a GDD of 488.7 instead of 3035 DAS which is regularly practiced, varied among the hybrids for better crop productivity. Pinnacle and DKC 9142 are recommended since they performed significantly better for all the various morphological, anatomical and physiological features of the crop.en-USnullThesis