Assessment of seed production potential of Teosinte (Euchlaena mexicana) under varying agronomic management practices in the central region of Nepal : A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Lincoln University

Abstract

Teosinte (Euchlaena mexicana) is a popular summer herbage crop in Nepal. While it has good seed production potential, the management for seed production is unknown. A two year study was undertaken in order to investigate teosinte seed yield and seed quality for different sowing dates, seed sowing rates and cutting management in the Terai region of Nepal. A seed development, a genotypic diversity and an economic study were also conducted. There were four different sowing dates (30 March, 30 April, 30 May and 30 June), four seed rates (20, 40, 60 and 80 kgha-1) and three cutting management treatments (uncut, once cut and twice cut) arranged in a spilt split plot design. The only certified variety of teosinte in Nepal, Sirsa was used for the study. Herbage yield of teosinte was affected by sowing date, seed rate and cutting management. Maximum herbage yield (HY) and dry matter yield (DMY) from a teosinte crop grown for seed production was obtained from the 30 April sowing together with the 60 kgha-1 seed rate and two cuts. There was a positive correlation of plant height, tiller number, leaf number and leaf area index (LAI) with DMY. The effect of the environment on both teosinte herbage and seed yield was studied. Higher herbage and seed yield were produced from early sown teosinte because the longer growing season allowed the accumulation of higher growing degree days (GDD). Five critical growth stages of teosinte were identified. The temperature and GDD requirements for each growth stage were 26.1○C (135○C days), 26.0○C (2189○C days), 24.1○C (2442○C days), 20.4○C (3049○C days) and 17.2○C (3150○C days) for emergence stage (GS1), vegetative stage (GS2), flowering stage (GS3), seed development stage (GS4) and seed maturity stage (GS5) respectively. Maximum seed yield (kgha-1) was obtained from the two earlier sowings (30 March and 30 April) in both years because early sown plants were taller, and had higher LAI and more tillers and cobs per plant, ears per cob and seeds per ear than later sown plants. In 2017, there was a non-insignificant effect of seed rate on seed yield because of natural thinning of plants due to heavy rainfall and wind which caused lodging in the early vegetative stage, but in 2018 the two lower seed rates (20 and 40 kgha-1) produced the highest seed yield. For cutting management, seed yield was higher for uncut plants in both years. Seed quality was tested for seeds harvested from different sowing dates, seed rates, cutting management and cob position on the plant. Over the two seasons of trials, seed harvested from the 30 March sowing at the two lower seed rates (20 and 40 kgha-1) and uncut plants resulted in higher germination percentage and thousand seed weight (TSW) in both years. There was a significant negative correlation between the sowing dates and germination percentage and a negative correlation between sowing dates and TSW because germination percentage and TSW were reduced with each delay in sowing. There was a positive correlation between TSW and germination percentage for different sowing dates for all cobs in 2017 (R2 = 0.77) (P>0.05) and 2018 (R2 = 0.80) (P>0.05). Seed quality was also affected by the cob position on the plant. When seeds were hand harvested separately from top, middle and bottom positioned cobs, higher quality seeds (germination percentage and TSW) were obtained from seed harvested from the top positioned cobs. Teosinte seeds physiological maturity (PM) was attained at 59 days after anthesis. Harvesting teosinte seeds from the top and middle positioned cobs on the plant recovered 78% of the total seed yield, while that from the middle and the bottom positioned cobs recovered 57% of the total seed yield. Therefore harvesting mature seeds from the top and middle positioned cobs is recommended to minimize loss of quality seed from shattering which would occur if harvesting was delayed until seeds from the bottom cobs were mature. A diversity study of teosinte was conducted for 18 teosinte accessions, 17 from CYMMIT Mexico and Sirsa, to identify if any of the introduced accessions could perform better than Sirsa in terms of herbage yield, seed yield and time to seed maturation. Out of 17 accessions, accessions 5, 7 and 12 out yielded Sirsa in terms of herbage yield, seed yield and were earlier to maturity. This preliminary result suggest a possible source of material for developing new teosinte varieties in Nepal better suited for farmer’s needs, particularly to reduce the length of time required to grow a seed crop. A separate study was conducted on seven seed lots of teosinte collected from different regions of Nepal. Hier¬archical cluster analysis based using morphological charecteristics gave two distinct clusters; cluster I (Makwanpur) from the midhills and cluster II (Sarlahi, Mohattari, Bara, Chitwan, Gaughat and Tikapur) from across the southern Terai. These two clusters suggest an agro ecological differentiation for teosinte genotypes grown in Nepal. An economic analysis conducted based on the total costs and income from the different management in this research study showed that the highest gross margin was obtained from the March and the April sowings at the 20-60 kgha-1 seed rates and none or one cuts. Taking one herbage cut was not detrimental to a farmer’s gross margin for seed production.