Plant population and shading studies in barley

Abstract

Two barley experiments are described in which a range of plant populations were shaded during different periods of development. Shading during the ear development period caused considerable reductions in grain yield, largely by reducing the number of grains per ear. Shading during the grain-filling period caused no reduction in grain yield. It is suggested that under conditions of these experiments there was probably a potential surplus of carbohydrate available for grain filling and that grain yield was largely determined by the storage capacity of the ears. The importance of the number of grains per ear as an indicator of individual ear capacity is emphasized.The effects of plant population on grain yield and its components are also examined. It is concluded that the number of grains per ear is the component having greatest influence on the decrease in grain yield at above-optimum populations and attention is again drawn to the possible importance of ear capacity. It is argued that on an area basis the number of grains per unit area may give a good indication of ear capacity. Examination of this parameter shows a close relationship with grain yield per unit area for both the shading and population treatments. It is particularly evident that a decrease in grain yield at high populations was associated with a comparable decrease in the number of grains per unit area. It is suggested that this decrease in grain number may be due to a lower production of total dry matter during ear development rather than an unfavourable partitioning of this dry matter between the ear and the rest of the plant. This lower production of total dry matter is attributed to the crop growth rates of the higher populations having reached their peak and then having declined before the end of the ear development period. This crop growth rate pattern, through its effect on grain number per unit area, is put forward as the basic reason why, in the final crop, grain yield per unit area decreases at above-optimum populations.

An investigation into the relations between some growth parameters and yield of barley

“…It is generally accepted that ear number per unit area and grain number per ear are determined at or before anthesis (Hesiop-Harrison, 1969; Kirby, 1973) implying that few fertile Glers die after anthesis and that most viable florets at anthesis set seed. The product of the above two factors, grain number per ucit are3, is sometimes claimed to be the major determinant of sink capacity and yield (Willey & Holliday, 1971 ;Gallagher, Biscoe & Scott, 1975). Gallagher et al (1975) suggest that variation in grain size is sufficiently small to be ignored.…”

Some effects of artificial variation in light interception, number of grains and husk constriction on the development of grain weight in normal and high-lysine barley

“…Such factors may include the post-anthesis mechanisms of number and size of endosperm cells, but possible pre-anthesis determination should also be considered. Thus grain weight as well as number of grains appears to be influenced by pre-anthesis variations in assimilate production achieved through light intensity (Willey & Holliday 1971a), leaf area (Williams & Hayes, 1977) or disease (Carver & Griffiths, 1981), although these effects could equally be due to effects on the availability of previously-stored assimilate for post-anthesis re-translocation. The suggestion that the flow of assimilate from the rachis phloem into the endosperm, rather than storage capacity per se, provides the restriction which is apparent within the ear (Jenner, 1976) has yet to receive support from other workers.…”

“…'Thinned early' (TE); Willey & Holliday (1971a) had shown that 50% shading of barley crops during the period prior to anthesis reduced ear size by about 2-5 grains per ear, so this treatment was devised to produce the converse effect, i.e. to increase the number of grains by increasing insolation during the same period.…”

Assessing the Consequences of Microbial Infection in Field Trials: Seen, Unseen, Beneficial, Parasitic and Pathogenic

“…For example, early leaves that later become the lower leaves of cereals may contribute effectively to plant establishment including tiller production and grain primordial number, but contribute nothing directly to grain fill. Many tillers later abort as the growth potential is matched to resources [30]. Thus, at any given time, leaves may have very different importance and this is reflected in their ability to express resistance to pathogen challenge.…”

“…Thus, at any given time, leaves may have very different importance and this is reflected in their ability to express resistance to pathogen challenge. Old leaves down-regulate defence mechanisms [30] and are thus vulnerable to pathogen attack or, more likely, saprophyte colonisation. In non-crop plants this may have few consequences, however for crops with greatly extended grain filling periods it could still have some detrimental effects.…”