The use of abscisic acid (ABA)-deficient mutants has contributed to elucidating the connection between the capacity to synthesize ABA and the drought response of plants. This review summarizes the present state of knowledge of two ABA-deficient mutants, recently isolated in sunflower (Helianthus annuus L.): nondormant-1 (nd-1) and wilty (w-1). The former is an albino mutant defective in carotenoid biosynthesis, inducào uyin vino tissue cullure. This mutation causes photobleaching or colorless pig."nt., absence of seed dormancy, and inability to accumulate ABA in cotyledons and leaves. Among albino mutants of dicotyledon species, nd-1 is the first mutânt characterized by ABA deficiency. The latter (w-1) is a genotype in which a spontaneous mutation confers a wilty phenotype. The wilting conditiôn of the nr-1 mutant is due to abnormal stomatal behaviour, associâted with low levels of endogenous ABA. Exogenou. agÀ rreatments can induce a phenotypic reversion of the mutant. Partial phenotypic reversion was also observed in mutânt scions grafted onto wild-type rootstocks. Detached leaves of w-1 were strongly dehydrated with a slight ABA increase. When water stress was imposed to potted mutant plants, significant changes in ABA content in stomal conductance were found only at very low water potentials. M: Moreover,w-1 started to accumulate ABA in the xylem sap and to close stomata when soil water content and leaf water potential were dramatically reduced. The results suggest thât the low endogenous AIIA levels and the inability to synthesize the hormone rapidly either in the leaves or in the roots are responsible for the high susceptibility of w-1 to water stress

Short-term effects of falling leafwater potential on photosynthesis and carbohydrate âccumulation in the leaves of four NS-sunflower hybrids were studied. Water stress was experimentally induced by holding the leaf and petiole submerged for 24 hours in 0, 0.05, 0.1, 0.2, 0.5, and 1.0 M sorbitol solutions. Increased concentrations of sorbitol, up to 0.2 M, induced a rapid decrease of relative water content (RWC) in the leaves of sunflower hybrids NS-H-26-RM, NS-Helios, NS-H-43, and NS-H-101. Rapidly applied water stress significantly reduced CO2 and light-saturated photosynthesis in the leaves already at 0.05 M sorbitol. The decline in net photosynthesis at decreased RWC in leaves was accompanied by a substantial decline in the apparent quantum yield. Primary photochemical reactions and electron trânsport appeared to be less affected by low RWC in leaves. Accumulation of soluble carbohydrates was increased under the effect of rapid water stress. The increased sucrose content could affect, through a feedback mechanism, the inhibition of photosynthesis. External wâter deficit induced the largest decline in the RWC and examined photosynthetic processes in NS-H-26-RM leaves, while the changes were the smallest in NS-H-101 leaves.

Attempts were made in sunflowers to develop plants from immature embryos instead of planting seed. Immature embryos of 12 days after flowering were dissected from seed- grown plants (SGP), and 1st cycle of embryo-raised plants (ERP) was obtained. When these plants were in the flowering stage, 12-day-old embryos were dissected, and 2nd cycle of ERP was raised. This procedure was followed for 5 cycles. Through this procedure, within 316 days, 5 cycles of ERP were completed. No variation was observed in plants of all 5 cycles of ERP except for male sterility. This methodology could be useful in the rapid development of inbred lines, fast conversion of inbred to cytoplasmic male sterile, or for any backcrossing programme as compared with the seed-to-seed cycle. Such rapid cycling of successive generations within a short period helps to achieve homozygosity early, which would accelerate the breeding cycle of crop plants.

A primary requirement of sunflower varieties for the UK is early maturity to avoid yield loss from infection by Botrytis cinerea of Scelerotinia sclerotiorum. Recombinant inbred lines selected in the UK following two cycles of inbreeding are being assessed in hybrid combination. The results of a trial of testcrosses produced between some French cytoplasmic male sterile lines (CMS) and the UK restorer lines are presented. Combining ability analysis indicated significant differences between both the CMS and restorer lines in their general combining abilities, but no differences in specific combining abilities for the yield-related characters. It was concluded that a number of these parental lines show potential as parents of hybrids for the UK. Analysis of correlations between the charâcters suggested that there were no barriers to obtaining hybrids with a favourable combination of traits for early flowering, short height, and high yield. TÏere was evidence of genetic control of resistance to Botrytis and Sclerotinia infection, and selection of such resistance should be an important breeding objective. The commercial varieties "Avante" and "Allegro" did not perform well in this trial.

Experimental hybrids were obtained by test cross during a backcross program, the purpose of which was the screening of new high oleic lines (HOL) in Metaponto. Seventeen hybrids were evaluated in an experimental field compared with 2 commercial hybrids and a high oleic synthetic line. Several tested hybrids showed good performances comparable with 3 testers. The hybrid 30503 showed high oleic content, an early flowering time, and interesting agronomical performances. The hybrid 30602 showed high oil content and high oleic acid rate in their seeds. These results showed that a screening for sunflower high oleic lines and hybrids with competitive performances could be carried out. Several parental HOL lines for the South Italy environmental conditions could be obtained.

The relationships of different seedling growth parameters with yield and yield components were studied in cultivated sunflower under non-saline (ECe2 dSm-1) and saline conditions (EGe 10 dSm-1). Inbred lines having shallow roots with low fresh weight and greater shoot length at the seedling stage produced higher seed yield under non-saline conditions. Seedling parameters showed very complex associations with seed yield under saline conditions. It was rather difficult to select high-yielding lines at the seedling stage under saline conditions, but oil yield could be increased indirectly through more seed weight, greater head diameter, and high oil content by selecting lines with shallow roots having more dry weight, and longer shoots having more fresh and dry weight. Selection of inbred lines having longer shoo6 with more fresh and dry weight under non-saline conditions appeared to be effective for achieving high seed-yielding lines for saline soils.

Field experiments were conducted for three years (1984-1936) during the summer season (Jan-Apr) at the University of Agricultural Sciences, Bangalore, India, to study the effect of moisture regimes, plant density, and fertilizer levels on grain yield of sunflower. Moisture regimes, plant density, and fertilizer levels independently influenced the seed yield. At this âgroclimatic condition prevailing during the summer season around Bengaluru, maximum seed field in sunflower can be realised by irrigating the crop at 0.6 CPE at the plant density of 55,555 plants ha-1. An increase in fertilizer levels increased the seed yield in sunflower, and maximum seed yield was realised at the higher fertilizer dose of 90:135:90 kg N: P:K ha-1. Water use efficiency in terms of seed field produced per unit amount of irrigation water applied increased with increased quantity of irrigation. An increase in plant density reduced water use efficiency. Water use efficiency increased with an increase in fertilizer levels.

Albugo tragopogonib (DC) S. F. Grey causes white blister rust, a disease restricted to leaves of sunflower. Oospores of A. tragopogords have, howeveç been associated with grey âreas on stems, petioles, and receptacles of sunflowers in Australia and Argentina. During tnê past two growing seasons, sunflower plantings in South Africa were subjected to early lodging. Disease Patterns and symptoms were studied in the field and in the laboratory. Sruisàlilè lesions occurred on stems of sunflower, which usually resulted in stem breakage. These lesions were heavily colonized by oospores of A. tragopogonir infection appeared to occur from the axils of lower leaves, and resulted in stem-breâkage during head expansion. Early lodging was recorded over a large geographical area, with losses as high as 80% in certain fields. Systemic infections with A. tragopogonis have also been observed, but are limited to a few plants.

A wilt disease of sunflower (Helianthus annuus L.) was observed during the summer of 1992 at the National Agricultural Research Centre, Islamabad. Disease incidence ranged from 5.0 to 10.0 percent. The pathogen was isolated from the infected sunflower plants and on the bâsis of its cultural characteristics, it was identified as Fusarium tabacinum (V. Beyma) W.Gams. This is believed to be the first report of this pâthogen on sunflowers in Pakistan.