Item

Seed yield and carbohydrate distribution in perennial ryegrass (Lolium perenne L.) and Italian ryegrass (Lolium multiflorum L.) seed crops

Holmes, Thomas
Date
2016-06-29
Type
Dissertation
Fields of Research
ANZSRC::070302 Agronomy
Abstract
A field experiment was conducted to quantify the carbohydrate distribution in perennial (Lolium perenne L.) and Italian ryegrass (Lolium multiflorum L.) seed crops from anthesis to harvest. To do this, first year crops of diploid perennial ryegrass (‘Samson’) and a diploid Italian ryegrass cultivar (‘Progrow’) were sown on 14th May and 16th September 2015. A subsequent application of Moddus® (a.i. 250 g/l Trinexapac ethyl) plant growth regulator at three rates (0, 1,600 and 3,200 ml/ha) was applied at Zakoks growth stage 32. Moddus® increased perennial and Italian ryegrass seed yield by approximately 29% from 1,600 ml/ha (1,651 kg/ha) to 3,200 ml/ha (2,134 kg/ha), with similar yields between 0 ml/ha (1,296 kg/ha) and 1,600 ml/ha. The seed yield increase in perennial and Italian ryegrass was achieved through increased number of seed produced per spikelets. The vegetative stem length in perennial and Italian ryegrass was reduced from 62 cm to 41 cm by application of 1,600 ml/ha of Moddus® and further reduced to 36 cm with 3,200 ml/ha. The perennial ryegrass’s stem component dry weight and water soluble carbohydrate (WSC) concentration were constant from anthesis through untill harvest. Despite Moddus® reducing the stem length and its storage capacity a large amount of WSC remained in the stem components. Perennial ryegrass had the capacity to fill and improve seed yield accumulating WSC simultaneously and converting this into starch up to harvest at 37 days after anthesis (DAA) with little or no remobilisation of WSC in the stem. Moddus® decreased Italian ryegrass’s stem components dry weight by 37% and WSC by 42% . The effect of Moddus® suggests the source and sink relationship between the stem and developing seed has been modified.The Italian ryegrass seed dry weight increased up to 7 DAA and declined until harvest with WSC and starch illustrating a similar pattern. When maximum seed weight, WSC and starch was achieved the stem component begun to decline. This demonstrates that Italian ryegrass stem may play a role in seed filling under conditions of limited assimilate supply with stem assimilate reserves remobilised to the developing seed. Moddus® reduced overall lodging at the highest rate of 3,200 ml/ha and delayed the onset of lodging at the lower rate. Lodging progressed more quickly and had a greater effect on perennial ryegrass than Italian ryegrass. Lodging reduced perennial ryegrass seed yield with less WSC in the seed of control plants of 0 ml/ha (49.91 mg) compared to the highest Moddus® treatment of 3,200 ml/ha (59.63 mg). Italian ryegrass showed similar seed WSC between the control (88.6 mg) and the two Moddus® treatments of 1,600 ml/ha (94 mg) and 3,200 ml/ha (85.5 mg). This showed the degree which two ryegrass species seed sinks can compete for available assimilates. The relative lower seed depression in lodged Italian ryegrass compared to the perennial indicates a higher compensation potential. The Italian showed the ability to partition more assimilate reserves from the stem and leaves to support seed growth and development.