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The sequence of flower and pod abscission on the main stem inflorescence of lupinus angustifolius

A. Pigeaire1, R. Delane2, M. Seymour3 and C. Atkins1

1Botany Department, University of WA, Crawley, 6009
Department of Agriculture, P.O. Box 110, Geraldton, WA, 6530
Department of Agriculture, PMB 50, Esperance, WA, 6450

Reproductive abscission in lupins is high, and only a few pods are usually retained at the base of the main stem inflorescence. Pod abortion is generally limited, fairly constant and occurs in the same region of the inflorescence where most pods are set (Delane et al., this conference), whereas prolific flower abortion occurs on the top portion of the inflorescence. Preliminary results from a study of the sequence of events leading to the precise location of flower and pod abortion for different treatments are reported here.


Trials incorporating sowing dates and plant densities were grown at Geraldton and Esperance, WA. At Geraldton ( red loamy sand; May-Oct. rain 375mm), one trial had 8 sowings (2 per week) during May, 1988. An adjacent trial had a further 4 sowings. At each sowing date, cv. Danja was grown at 22 and 44 plants.m-2 (hand thinned). At Esperance (grey sand/clay at 40cm; May-Nov. rain 385mm) there were 4 sowing dates at weekly intervals (44 plants.m-2 only). From the start of anthesis the phenological stage of each reproductive site on the main inflorescence was recorded weekly on 12 plants/plot, the timing of flower opening and abscission, and pod formation and abscission was determined.

Results and discussion

The sequence of events on the raceme of the main inflorescence during anthesis and pod setting were:acropetal flower opening progressed rapidly, with a peak rate of flower opening of almost 2 of flowering continued along the raceme, but the progression of pod initiation ceased.Abortion of flowers began just above the last initiated pod. abortion of flowers then progressed towards the top of the raceme and at the same time, pods aborted on the lowest part of the raceme. Plant density did not affect inflorescence size, or the progression of flower opening, but pod initiation ceased earlier at high plant density (Figure 1). A similar number of pods aborted on all treatments and the zone of pod abortion was located at a different height on the raceme according to the position at which pod initiation ceased. Therefore, the difference between density treatments in the final number of pods observed was determined by the timing,and therefore the position on the raceme, at which the abscission process began.Once flower and pod abscission had begun, it exhibited the same pattern for all treatments.

Figure 1. Progression of flower opening and pod initiation on the main inflorescence of L. angustifolius.

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