In this article we will discuss about the growth and development of pigeonpea crop.
Germination and Seedling Growth:
Germination of pigeonpea is slower compared with cowpea, greengram and blackgram. Although, emergence is progressively reduced when seed is sown below 5 cm, some seedlings can emerge from as deep as 30 cm.
Growth of pigeonpea seedlings is relatively slow, a factor of potential advantage where pigeonpea is intercropped with rapidly growing cereals but may be disadvantage in a sole crop where weed competition is severe. The slower growth rate appears to be due mainly to smaller seedling leaf area.
Under favourable conditions, LAI increases exponentially until the canopy starts to close, at which time the older by then the shaded leaves begin to senesce and abscise. Therefore, the rate of leaf area accumulation slows and LAI ultimately reaches maximum when the rate of new leaves development be balanced by the loss of older leaves. A pigeonpea crop may reach maximum LAI prior to flowering, during flowering or even during pod filling depending upon variety, location and sowing date.
Usually, maximum LAI is of the order of 4-6. Biomass accumulation is essentially a linear function of the amount of PAR intercepted by the crop canopy, which in turn is a function of LAI, at least during vegetative growth.
During reproductive stage, the relationship between LAI and the proportion of PAR intercepted by the canopy becomes less apparent and floral structures and developing pods intercept an increasing proportion of incident radiation.
In canopies where an LAI more than 6 is necessary for complete interception of PAR during vegetative stage, complete interception of PAR could be achieved with LAI as low as 2.5 subsequent to flowering.
Changes in LAI with time closely parallel to changes in leaf dry weight. Maximum LAI recorded at Hyderabad (AP) is 12.6. However, maximum LAIs of medium duration varieties in normal season at Hyderabad usually range from 3 to 6 and in postrainy season crop sown around October, LAIs rarely exceed 1.0 even with high population. The NAR usually decline through most of the growth period. They are around 50 g m-2 wk-1. In most cultivars, the NAR increase towards the end of reproductive phase.
Onset of flowering in pigeonpea depends on the sensitivity of genotypes to day length and temperature. Most varieties behave as quantitative short day plants, with the time from sowing to flowering longest for sowings made prior to the summer Solstice and shortening progressively as sowings are delayed into shortening days towards the winter Solstice.
Very early flowering varieties appear to be relatively photoinsensitive, even day neutral. In these varieties, temperature predominantly influence flowering. Optimal temperature for flowering appears to be around a mean daily temperature of 24°C.
Most pigeonpeas are more or less indeterminate in flowering habit with auxiliary flowering racemes forming along the apical portions of branches. Some short duration types are morphologically determinate and basipetalus, although within racemes flowers open subsequently. Determinate types have fewer racemes but more flowers leading to longer duration of flowering in individual racemes than in indeterminate types.
Flowering may be confined to a three-week period or may continue for several months depending on genotype, environment and plant density. High population reduces branching and increase synchrony of flowering, particularly in more determinate types.
Conversely, flowering period is, generally, longer in indeterminate types and may be extended in less dense sowings and under long day/warm temperature conditions and environmental conditions that increase floral abortion such as heat waves, drought stress or cloudy weather.
Most flowers are shed without setting pods. Physical removal of flowers and young pods stimulates flower production but has no effect on final yield. Number of pods per plant is strongly related to assimilation during early pod growth, through effects on pod formation, for the first two weeks after anthesis and on pod retention for the next two weeks.
The HI of pigeonpea ranges from 10 to 52 per cent depending upon genotype, environment and agronomic management. The HI of pigeonpea is low (25%) relative to cereals and other legumes such as soybean. This is particularly so for long duration types traditionally grown in India. In contrast, HI of soybean approaches 40 per cent.
The HI in pigeonpea tends to be greater in early flowering and short duration types. Interestingly, long duration types when grown as intercrop, their HI is much improved even though their absolute seed yield is lower than that of equivalent sole crops, commonly by 20-50 per cent.
In tropical grain legumes, HI is a function of relative durations of the vegetative and reproductive phases and during the reproductive phase, relative partitioning of current assimilates and the degree of remobilisation of stored assimilate to seed. Thus, HI is particularly enhanced where the duration of reproductive growth represents a large proportion of total growth.
Thus, in early flowering types and late sowings which because of strongly inductive photothermal conditions, encourage precocious flowering. An analogous situation exists with the intercrop, where the early vegetative development, which occurs in sole crop, is suppressed by the component crop.
In several species, the direct effects of photothermal regime on assimilate partitioning after start of flowering combine with its indirect effects on relative duration of reproductive growth to ensure that HI is maximised when crops are grown under photothermal conditions which favour rapid ontogenetic development.
The result is that there is frequently a generalised negative relationship between HI and crop duration that can also be demonstrated in pigeonpea.