ITEMS FROM ROMANIA

RESEARCH INSTITUTE FOR CEREALS AND INDUSTRIAL CROPS - I.C.C.P.T.

Fundulea, 8264, jud. Calarasi, Romania.

Dark-induced senescence as a tool in breeding for the optimization of senescence pattern.

N.N. Sãulescu and Gh. Ittu.

Senescence is one of the most important (and neglected) processes in plant development and agriculture (Thomas and Villiers 1996). Differences in senescence patterns are known in many crops, but progress in optimizating senescence rate has been slow in wheat, where senescence often is confounded by the effects of diseases, earliness, and stress tolerance.

The onset of senescence can be induced by many different factors, both internal (age) and external. Environmental stresses such as temperature, drought, poor light or nutrient supply, and pathogen attack all will result in premature initiation of senescence. Although the original signals that act to regulate senescence under these conditions may be different, the processes involved are likely to be the same (Buchanan-Wollaston, 1997). Recent results show that transcripts accumulate during the dark-induced senescence of primary foliage leaves, and also during senescence of flag leaves collected from the field. Other research shows mRNA changes during dark incubation of detached leaves with both stress-induced changes and with changes found under normal leaf senescence. A senescence-associated gene of Arabidopsis thaliana was shown to be induced strongly by age, but also by dark exposure and ABA treatment. The promoter that controls expression of the LSC54 gene from Brassica napus during senescence, is not only highly induced during natural senescence, but also shows increased activity in response to wounding and during dark-induced senescence. These results suggest that genetic differences in response to dark induced senescence can provide information on the genetic systems involved in normal and/or stress-induced senescence.

We first tested this hypothesis in maize, where we found that dark-induced senescence symptoms were correlated with field 'stay green' scores (the percentages of green plants at physiological maturity) of 14 maize hybrids (Saulescu et al. 1998).

We also found large and visible genotypic differences in dark-induced senescence in wheat by exposing seedlings of wheat cultivars at the 2-leaf stage to continuous darkness. During a recent visit to Oregon State University, chlorophyll content was measured in the first leaf of 11 wheat cultivars using a Minolta Chlorophyll Meter SPAD 502, after 0, 42, 114, 166, 212, and 284 hours of dark treatment. Chlorophyll content decreased linearly with dark treatment duration. Regression slopes varied significantly among cultivars, from - 0.0476 SPAD units/hour in TAM 200 to almost double (- 0.0861 SPAD units/hour) in Jagger. The best discrimination among cultivars was obtained after 8-10 days of dark treatment. At this stage, even visual observations can discriminate easily between fast and slow senescing genotypes (Sulescu and Kronstad, 1998).

We suggest that a seedling test for dark-induced senescence might be used in breeding programs to accelerate genetic progress for optimization of senescence processes.

References.

Sãulescu NN, Ciocazan I, and Lazar C. 1998. Genotypic differences in dark induced senescence are correlated with field "stay green" scores in maize (Zea mays L.). Rom Agric Res In press.

Sãulescu NN and Kronstad WE. 1998. Genotypic differences in leaf chlorophyll loss during dark induced senescence in seedlings of winter wheat (Triticum aestivum L.). Rom Agric Res In press.

Stability of response to Fusarium head blight in a collection of Romanian winter wheat genotypes under artificial inoculation.

Mariana Ittu, N. N. Sãulescu, and Gh. Ittu.

The stability of resistance to FHB was studied under artificial field inoculation in eight Romanian winter wheat genotypes with different levels of resistance, and in the Chinese source of resistance Sumai 3 (spring wheat). The relative weight of the inoculated spikes (RWIS) was recorded between 1990 and 1997, as a percentage of the weight of the healthy spikes. The amplitude of variation and variance(s) across years, coefficients of regression (b) on average values of all entries, and deviations from regression were used as stability parameters. All stability parameters revealed large differences among cultivars in the stability of their RWIS response under artificial inoculation in the field. Both amplitude of variation and variance across years agreed in classifying F201R (resistant), F4549W (medium resistant), and Fundulea 4 (susceptible) as the most stable entries. Fundulea 29 and F116L had the most variable responses. Stability was not associated with average RWIS, because different stabilities were found among entries of similar resistance. On average, regression of all entries explained only a small part of the total RWIS variation and, therefore, was considered less suitable for studying RWIS stability.

Reference.

Ittu M, Sãulescu NN, and Ittu G. 1997. Stability of response to FHB in a collection of Romanian winter wheat genotypes under artificial inoculation. In: Conf Proc 'Approaches to improving disease resistance to meet future needs: Airborne pathogenes of wheat and barley'. 11-13 November, 1997. Praha:56-60.

Triticale breeding.

Gh. Ittu, N.N. Sãulescu, Mariana Ittu, annd P. Mustãtea.

A new cultivar Titan was released in Romania in 1998 and is the first Romanian winter triticale cultivar. Titan has short straw with improved resistance to lodging, has better sprouting resistance, heads 2-3 days earlier and has better fertility of the spike and higher test weight than the main commercial cultivars Plai and Colina. Titan was tested under the name 191TR2-12 or TF94-1. Titan was selected from the complex cross '12TK2-1/121TK2-3//Plai', where 12TK2-1 is a line derived from the cross 'M-ARM"S"/274-230//AD206', 121TJ2-3 is a selection from 'Sadovo1 (6x wheat)/Lc 79-70 (rye inbred)//AD206', and Plai is a released Romanian winter triticale cultivar. In 44 yield trials (during 4 years), Titan outyielded the recently released Plai and Colina by 6.8 %.