Browsing by Author "Mullins, C.E."

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Root-shoot growth interactions of sorghum (sorghum bicolor l moench) in response to mechanical impedance
(2000) Rwehumbiza, F.B.R.; Mullins, C.E.
Soil mechanical impedance has a widespread influence on plant organ expansion, penetration, and growth. Studies on root-shoot intera'ctions in relation to mechanical impedance have only investigated the effect on shoots of mechanical impedance imposed on roots. The aim of the reported study was therefore to fill the identified iap in knowledge, including an investigation into all root-shoot interations in response to mechanical impedance. Individual pregerminated sorghum (Sorghum bicolor L. Moench) seeds cultivar ICSV-I12 were grown for 8 days in a growth room in seven replicate cylinders per treatment. Treatments were: (a) impeded root and impeded shoot (II), (b) impeded root and unimpeded shoot (lU), (c) unimpeded root and impeded shoot (VI), and (d) the control, in which both the root and shoot systems were unimpeded (UU). The impeding growth medium was a mixture of sand and vermiculite packed to give a penetration resistance (PR) of 1.18 MPa below the seed and 0.32 MPa above the seed. Control cylinders were completely packed with expanded vermiculite to a bulk density of 0.2 Mg m-3 giving aPR ofO. 025 MPa. Matnc suction was 5.kPa in both media. Results were that: (i) Impedance tg the shoot significantly (P < 0.05) delayed emergence, more so when the root was, also impeded. (ii) Shoots emerging through a mechanically impeding layer, had significantly greater extension rates after emergence than unimpeded ones. (iii) Mesocotyls became significantly thicker only when (he root systems were impeded. (iv) Impeding the shoot system, significantly increased root extension rate. (v) The length of the first internode, the number of leaves and the spacing of lateral roots were not changed by any of the treatments. Root-shoot signalling is suggested as one ofthefactors responsiblefor these interactions. Generally, our findings indicate that mechanical impedance which may be caused by sUrface crusting and hardsetting soils and shallow tilth achieved with a hand hoe results in poor crop establishment and probably total. crop failure.
A Technique for Controlling Matric Suction on Filter Papers used in seed Gennination Tests, Imbibition, root and shoot Growth studies
(1998) Rwehumbiza, F.B.R.; Mullins, C.E.
Moist filter papers are widely usedfor seed gennination tests but their water confent and matric suction are not usually controlled. A technique for controlling filter paper matric suction is described and usedfor germination studies involving fresh and aged sorghum seed (Sorghummcolor (L) Moench). Filter papers wetted to matric suctions of 0.1 ,land 10 kPa were used to study germination, root and shoot growth rate offour cultivars (M35-1, ICSV-1l2, CSH-9 & CSH-ll) of sorghum at 25°C. Time to germination, root and shoot growth were all affected by the increase in matric suction from either 0.1 to 1, or 1 to 10 kPa. Root and shoot emergence ratefrom seeds, decreased with increasing matrie suction. The increase in matric suction resulted in significant reductions (P= O. 05) in final root and shoot length. Final germination percentage was not affected by variation§ in matric suction. Ageing delayed shoot emergence. Seedlings with emetged shoots were significantly fewer at 10 kPa as compared to 1 kPa only for aged seed, and for all cultivars except Icsv-i 12. A link between matrie suction, seed-liquid contact area and the rate of water uptake by seed is demonstrated. We conclude from this study: that changes in the matric suction on filter paper even at the wet end will cause variations in gennination rate and therefore ought to be controlled during germination tests. Seed tests separated in time and space can not be compared iffilter paper matric suction is not controlled.