In a primary care setting the combination of dermoscopy and short-term SDDI reduces the excision or referral of benign pigmented lesions by more than half while nearly doubling the sensitivity for the diagnosis of melanoma.
The influence of terminal drought on the seed growth of 3 chickpea
(Cicer arietinum L.) genotypes was examined in a field
experiment at Merredin, Western Australia. Tyson, a small-seeded desi
cultivar, ICCV88201, a desi breeding line (sister line to the recently
released Sona cultivar) with medium-sized seed, and Kaniva, a kabuli cultivar
with large seed, were grown under rainfed and irrigated conditions. In the
rainfed plots, leaf water potential had decreased from above –1.2 MPa to
about –2.5 MPa and net photosynthesis from 21 to 29 µmol
CO2/m2. s to below 10
µmol CO2/m2.s, by the
time seed filling commenced. Rainfed plants had significantly fewer pods than
irrigated plants, regardless of genotype. In rainfed plants average seed
weight was reduced by 19, 23 and 34% and yield by 74, 52 and 72%
in Tyson, ICCV88201, and Kaniva respectively. Individual pods were tagged at
pod set on previously-selected representative plants and were weighed
separately from the rest of the plant over 6 subsequent harvests so that the
rate and duration of seed fill could be measured. Genotypic differences in the
maximum rate of seed fill were found to exist in chickpea. In both irrigated
and rainfed conditions, Kaniva had the highest maximum rate of seed fill
followed by ICCV88201 and Tyson. Both the rate and duration of seed growth
were reduced in the rainfed plants, regardless of genotype. Reductions in the
dry weight of the pod shell suggest that the remobilisation of dry matter from
the pod may contribute 9–15% of the seed weight in rainfed
chickpea.
Abstract. Water-repellent ('non-wetting') soils are a major constraint to agricultural production in southern and south-west Australia, affecting >10 Mha of arable sandy soils. The major symptom is dry patches of surface soil, even after substantial rainfall, directly affecting agricultural production through uneven crop and pasture germination, and reduced nutrient availability. In addition, staggered weed germination impedes effective weed control, and delayed crop and pasture germination increases the risk of wind erosion. Water repellency is caused by waxy organic compounds derived from the breakdown of organic matter mostly of plant origin. It is more prevalent in soils with a sandy surface texture; their low particle surface area : volume ratio means that a smaller amount of waxy organic compounds can effectively cover a greater proportion of the particle surface area than in a fine-textured soil. Water repellency commonly occurs in sandy duplex soils (Sodosols and Chromosols) and deep sandy soils (Tenosols) but can also occur in Calcarosols, Kurosols and Podosols that have a sandy surface texture. Severity of water repellency has intensified in some areas with the adoption of no-till farming, which leads to the accumulation of soil organic matter (and hence waxy compounds) at the soil surface. Growers have also noticed worsening repellency after 'dry' or early sowing when break-of-season rains have been unreliable.Management strategies for water repellency fall into three categories: (i) amelioration, the properties of surface soils are changed; (ii) mitigation, water repellency is managed to allow crop and pasture production; (iii) avoidance, severely affected or poorly producing areas are removed from annual production and sown to perennial forage. Amelioration techniques include claying, deep cultivation with tools such as rotary spaders, or one-off soil inversion with mouldboard ploughs. These techniques can be expensive, but produce substantial, long-lasting benefits. However, they carry significant environmental risks if not adopted correctly. Mitigation strategies include furrow-seeding, application of wetting agents (surfactants), no-till with stubble retention, on-row seeding, and stimulating natural microbial degradation of waxy compounds. These are much cheaper than amelioration strategies, but have smaller and sometimes inconsistent impacts on crop production. For any given farm, economic analysis suggests that small patches of water repellency might best be ameliorated, but large areas should be treated initially with mitigation strategies. Further research is required to determine the long-term impacts of cultivation treatments, seeding systems and chemical and biological amendments on the expression and management of water repellency in an agricultural context.
In the Mediterranean-type environment of south-western Australia, pod filling
of chickpea occurs when net photosynthesis and nitrogen fixation is low as a
result of the onset of terminal drought. Remobilisation of carbon (C) and
nitrogen (N) from vegetative parts to developing seed may be an important
alternative source of C and N for seed filling. The contribution of stored
pre-podding C and N to seed filling was studied by labelling the vegetative
tissues with the stable isotopes, 13C and
15N, prior to podding and following their subsequent
movement to the seed. In ICCV88201, an advanced desi breeding line, 9%
of the C and 67% of the N in the seed were derived from pre-podding C
and N in well-watered plants compared with 13% of the seed C and
88% of the seed N in water-stressed plants. Furthermore, the
contribution of pre-podding C and N was higher for earlier set compared with
later set seeds. Pre-podding C and N were derived predominantly from the
leaves with relatively little from the stems, roots, and pod walls. Genotypic
variation in remobilisation ability was identified in contrasting desi (Tyson)
and kabuli (Kaniva) cultivars. In well-watered Tyson, 9% of the seed C
and 85% of the seed N were remobilised from vegetative tissues compared
with 7% of the seed C and 62% of seed N in well-watered Kaniva.
Water deficit decreased the amount of C remobilised by 3% in Tyson
compared with 66% in Kaniva, whereas the total amount of N remobilised
was decreased by 11% in Tyson and 48% in Kaniva. This was
related to the maintenance of greater sink strength in Tyson, in which the
number of filled pods was reduced by 66% in stressed plants compared
with a 91% decrease in Kaniva. This indicates that better drought
tolerance in desi genotypes is partly a consequence of better remobilisation
and higher pod number. These studies show that C and N assimilated prior to
podding can supplement the supply of current assimilates to the filling seed
in both well-watered and water-stressed chickpea. Remobilisation of
pre-podding N is an essential source of N for seed filling irrespective of
environmental stress.
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