Current and future strategies in breeding lentil for resistance to biotic and abiotic stresses

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  • Euphytica73 : 1 27-135,1994 .

    127

    1994 Kluwer Academic Publishers . Printed in the Netherlands .

    Current and future strategies in breeding lentil for resistance to biotic and

    abiotic stresses

    W. Erskine', M. Tufail2 , A. Russell', M. C. Tyagi4 , M. M. Rahman 5 and M. C. Saxenal

    1 ICARDA, P O. Box 5466, Aleppo, Syria;

    2

    Pulses Research Institute, Ayub, Faisalabad, Pakistan ;

    3

    Department

    of Scientific and Industrial Research, Private Bag, Christchurch, New Zealand; 4Genetics Department, Indian

    Agricultural Research Institute (JARI), New Delhi 110 012, India, and 5Regional Agricultural Research Station,

    Ishurdi 6620, Pabna, Bangladesh

    Key words : ascochyta, cold, drought, lentil, Lens, resistance, rust, tolerance, wilt

    Abstract

    Lentil production is limited by lack of moisture and unfavorable temperatures throughout its distribution . Waterlog-

    ging and salinity are only locally important . Progress has been made in breeding for tolerance to drought through

    selection for an appropriate phenology and increased water use efficiency and in breeding for winter hardiness

    through selection for cold tolerance .

    The diseases rust, vascular wilt, and Ascochyta blight, caused by Uromyces viciae fabae, Fusarium oxysporum

    f. sp . lentis, and Ascochyta fabae f . sp . lentis, respectively, are the key fungal pathogens of lentil . Cultivars with

    resistance to rust and Ascochyta blight have been released in several countries and resistant sources to vascular

    wilt are being exploited . Sources of resistance to several other fungal and viral diseases of regional importance are

    known. In contrast, although the pea leaf weevil (Sitona spp.) and the parasitic weed broomrape (Orobanche spp .),

    and to a lesser extent the cyst nematode (Heterodera ciceri), are significant yield reducers of lentil, no sources of

    resistance to these biotic stresses have been found . Directions for future research in lentil on both biotic and abiotic

    stresses are discussed .

    Introduction

    In West Asia and North Africa, lentil (Lens culinaris

    Medikus) is winter-sown at elevations below about 850

    meters and is usually spring-sown at higher elevations,

    representing two contrasting agro-ecological regions .

    Diagrams of the climate at sites representing these two

    agro-ecological regions are given as Figure 1 (Mueller,

    1982). In these areas the crop is grown in drier and cold-

    er environments than other food legumes . These agro-

    ecological regions are characterized by wet winters,

    springs with rapidly rising temperatures and hot, dry

    summers. The major limiting factors to crop growth are

    low moisture availability and high temperature stress

    in spring, and, at high elevations, cold temperatures in

    winter. Consequently, selection for tolerance to these

    abiotic stresses is of prime concern to lentil breeders

    in both agro-ecological regions .

    By contrast, in South Asia where 50% of lentil is

    sown (Anonymous, 1990) biotic stresses, particularly

    diseases such as rust (Uromyces viciae fabae), vascular

    wilt(Fusarium oxysporum f. sp . lentis), and Ascochyta

    blight (Ascochyta fabae f. sp . lentis) are major limiting

    factors addressable by breeding . Moisture and temper-

    ature stresses are also important in limiting yield . A

    climato-diagram for a representative lentil producing

    site in South Asia is also given in Figure 1 . The rel-

    ative importance of various biotic and abiotic stresses

    globally on lentil is indicated in Saxena (1993) and

    Johansen et al . (1994) .

    This paper addresses current and future strategies

    of lentil breeding for resistance to abiotic stresses such

    as the extremes of temperature, moisture stress and to

    biotic stresses focusing primarily on fungal pathogens .

  • 128

    Aleppo (390m) 399mm

    Mean temperature (C)

    Rainfall total (mm)

    50

    Sep

    Temp

    -f- Rainfall

    Oct Nov

    l

    Dec Jan Feb Mar Apr1 May Jun Jul, Aug

    SW

    S

    Hw H

    Kanpur (127m) 823mm

    Mean temperature (C)

    so

    100

    80

    60

    40

    20

    0

    0

    SepOct, No Dec

    Jan Feb Mar Apr May Jun Jul Aug

    S

    1

    H

    Fig. 1. Climato-diagrams showing monthly mean temperatures (C) and rainfall totals (mm) in Aleppo, Ankara and Kanpur, which are

    representative of the three major agro-climatic regions of lentil production in the developing world. The elevation above sea level (m) and

    long-term mean rainfall totals (mm) are given . Typical dates for sowing (S) and harvest (H) are shown; in Ankara dates for winter-sowing (Sw)

    and harvest (Hw) are also shown .

  • Abiotic stresses

    Temperature

    Low temperature

    In the agro-ecological region of lowland Mediterranean

    and south Asia, winters are usually mild . Low temper-

    ature is a factor limiting lentil production, but is less

    important than low moisture availability. For exam-

    ple, at Tel Hadya (280 m.a .s .l .) total seasonal rainfall

    accounted for 80% of the variance in mean seed yield

    and the addition of the number of frost nights to the

    model lifted the variance of seed yield accounted for to

    93%, with each frost night reducing seed yield by an

    average of 15 .5 kg ha t (Erskine & El Ashkar, 1993) .

    Late frost is known to damage early-sown plants more

    than late-sown material (ICARDA, 1990) .

    In contrast at higher elevations, where lentil is

    spring-sown because of the severe winter cold, exper-

    iments in Turkey have shown that autumn-sown lentil

    can yield 50% to 100% more than the traditional spring

    sowing using cultivars with winter hardiness (Sakar et

    al., 1988) .

    Winter survival of lentil often requires tolerance

    to factors other than cold : e.g ., frost-heaving, water-

    logging, and diseases such as various root pathogens

    and Ascochyta blight . Cultural practices also strongly

    affect winter survival, as do frost, and disease and pest

    attack prior to the onset of winter . In short, a complex

    of factors is involved in winter survival (Murray et al .,

    1988), and a myopic preoccupation with cold tolerance

    is to be avoided . Screening in lentil for winter hardi-

    ness has been confined to evaluating survival in the

    field (Erskine et al ., 1981). No recourse has been made

    to using associations with other morphological, phys-

    iological and/or chemical traits or controlled environ-

    ment facilities . In other species, controlled freeze tests

    and measurements of plant moisture offer the breeder

    the best means of predicting cold tolerance, but final

    evaluation must still be done in the field (Murray et al .,

    1988). The variation of the field screening environment

    caused by large differences in winter cold between sites

    and seasons and local differences in snow cover and

    soil fertility make progress slow . Use must be made

    of many different locations each season . A search for

    normally snowless, cold, winter areas for screening is

    warranted .

    Despite the problems of field screening, several

    winter hardy lentil cultivars have been released in

    Turkey (Sakar et al ., 1988) and sources of winter har-

    1 29

    diness registered in the USA (Spaeth and Muehlbauer,

    1991). A world collection of 3592 lentil accessions

    was screened for cold tolerance near Ankara, Turkey

    over a severe winter with temperatures going as low as

    - 26.8 C with 47 days of snow cover (Erskine et al .,

    1981). A total of 238 accessions were found undam-

    aged by the cold winter with origins mostly from Chile,

    Greece, Iran, Syria, and Turkey, where natural selec-

    tion for cold tolerance had occurred . Further confirma-

    tion of their cold tolerance was found in joint screen-

    ing in Italy ; and, as a result, a nursery of cold tolerant

    sources is distributed to cooperators annually in the

    Food Legume International Testing Program . Pure line

    selection and mass selection of landraces has, and will

    continue to have, a role in selecting for winter hardi-

    ness .

    Additional sources of winter hardiness are being

    sought at ICARDA within Lens culinaris ssp . oriental-

    is (see Cubero, 1981), the distribution of which spans

    areas of severe winter cold . As this species is crossable

    with the cultigen, utilization of new genetic variation

    for winter hardiness should be simple.

    A major effort is now underway at ICARDA to

    recombine sources of winter hardiness with other

    attributes for high elevation areas in simple crosses,

    and segregating populations with one winter hardy par-

    ent are being distributed in the Food Legume Interna-

    tional Testing Program . There are no reports on the

    inheritance of cold tolerance in lentil, but collabora-

    tive research between the USA, Turkey, and ICARDA

    on this topic is in progress . In view of the difficulty

    in measuring winter hardiness due to environmental

    variation, it may be useful to study linkages between

    molecular markers (allozymes, RFLPs and RAPDs)

    and winter hardiness in order to explore the useful-

    ness of marker-assisted selection . Efforts have begun

    at ICARDA to recombine various sources to increase

    the level of winter hardiness using simple recurrent

    selection facilitated with a new source of cytoplasmic-

    genetic male sterility (Muehlbauer, pers . comm .) .

    High temperature

    High temperatures are encountered by lentil in the

    major production regions mainly during the reproduc-

    tive stage of growth, usually accompanied by condi-

    tions of low moisture availability . Initial efforts to sep-

    arate the effects of heat and water stresses in the field

    using supplemental irrigation treatments and heat treat-

    ments during the reproductive growth stage by cover-

    ing with a plastic tunnel have been made at ICARDA

  • 1 30

    (ICARDA, 1989). The paramount importance of mois-

    ture stress in a dry season was established and a heat

    treatment of about 10C resulted in no change in total

    biomass but a reduced distribution of dry matter into

    reproductive growth . Refinement of the technique for

    providing heat stress is required .

    Water

    Water deficit - drought

    In lowland Mediterranean environments lentil is usu-

    ally sown in the zone with between 300 to 400 mm

    annual precipitation in the months of December and

    January. The early stages of vegetative growth are

    restricted by low radiation and temperature, but this

    is the time of increasing rainfall and low evaporative

    demand. From March until maturity in May, the crop

    experiences increasingly strong sunshine, a rapid rise

    in maximum temperature (see Figure 1), a fall in rain-

    fall, and high evaporative demand. Drought stress is

    common during this period, which coincides with the

    phase of reproductive development in the crop, and

    as a consequence yields are frequently low. The key

    importance of moisture in a lowland Mediterranean

    environment is illustrated by the fact that total season-

    al rainfall accounted for 80% of the variance in mean

    seed yield at a single site over several seasons (Erskine

    & El Ashkar, 1993) . Although lentil is grown in drier

    environments than other food legumes in West Asia

    and North Africa, the drought strategy of the species is

    typically one of drought avoidance with forced senes-

    cence and crop maturity induced by conditions of high

    temperature and/or drought stress .

    The breeding program at ICARDA uses simulta-

    neous yield tests at sites spread along a rainfall cline .

    Selection at these sites has resulted in increases in water

    use efficiency.

    Other approaches to screening for drought toler-

    ance have been tried on lentil at ICARDA with varying

    degrees of success. Testing performance across sites

    contrasting in rainfall presupposes that sites differ in

    moisture availability and not in soil or other factors.

    To avoid problems, moisture availability may be con-

    trolled at a single site . At a dry site water may be added

    in varying amounts by a line-source sprinkler system,

    or at a wet site a rain-out shelter may be used to exclude

    moisture.

    Initially at ICARDA, the approach to drought

    screening was through the exclusion of moisture at a

    wet site using plastic sheets on the soil in October and

    November, until a particular rainfall total was passed

    (e.g., 50, 100 mm), prior to sowing . An additional

    treatment of supplementary irrigation was applied, cre-

    ating different levels of moisture supply at a single site

    (ICARDA, 1983 and 1984) . More recently we have

    used a line-source sprinkler system at a dry site and

    found that in a dry season (180 mm), 49% of the vari-

    ation in seed yield among lines was accounted for by

    variation in flowering time . Drought escape was clearly

    the key response to drought and, for severely drought-

    prone areas, selection for early flowering is required

    (Silim et al ., 1993). But, while the line-source sprin-

    kler system is useful in identifying differences between

    potential parents in response to moisture, it cannot be

    used for single plant selection .

    As another screening method, late sowing to screen

    for drought tolerance was tried assuming that the crop

    would experience severe drought and heat stress as it

    matured late under conditions of low moisture avail-

    ability and high temperature. However, vegetative and

    phenological development was abnormal even in wet

    seasons, because late sown plants were strongly affect-

    ed by both temperature and photoperiod . Selection

    under these conditions was clearly for many charac-

    ters other than drought tolerance, and late sowing as a

    method of drought screening was abandoned .

    In view of the slow progress in other crops in

    response to direct selection for yield under drought,

    analytic breeding has been suggested, whereby selec-

    tion is practiced on another trait, which is strongly

    associated with yield under drought and has a higher

    heritability than yield itself (Richards, 1987) . Although

    it is facile to expect any single character to determine

    yield under drought stress, in view of the variation

    of stresses and the complexity of yield development,

    many such characters have been proposed for other

    crops (Srivastava et al ., 1987). In lentil, we have exam-

    ined traits associated with yield under rainfed condi-

    tions and found that early vigor was strongly correlated

    with biomass and seed yield (Silim et al ., 1992). The

    association of isozyme and RAPD markers with yield

    under drought conditions and the feasibility of marker-

    assisted selection for drought is also worth exploring .

    Selection for deep rooting has been advocated to

    increase food legume productivity under moisture lim-

    iting conditions (Buddenhagen & Richards, 1988) . In

    the lowland mediterranean environment the lentil is

    favored in rotation with wheat over many other legumes

    because the crop does not utilize all the moisture stored

    in the soil profile, leaving some residual stored mois-

    ture for the succeeding wheat crop (H . Harris, pers .

  • comm.) . While an increase in lentil rooting depth may

    result in increased lentil yield, it might, however, be at

    the expense of wheat productivity.

    In another approach to screening for drought toler-

    ance the differential growth response of genotypes to

    osmotic stress in a solution containing different levels

    of polyethylene glycol (PEG) as osmoticum is being

    investigated and comparisons with field reaction to

    drought being made (N . Haddad and F.J . Muehlbauer,

    pers. comm.) . The results are not yet available...